'{-L'NO'f.  STATE  GEOLOGICAL  SURVEY 


3  3051  00006  4158 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  Illinois  Urbana-Champaign 


http://archive.org/details/surfacesubsidenc17youn 


STATE  OF  ILLINOIS 

STATE  GEOLOGICAL  SURVEY 

FRANK   W.  DE  WOLF,  Director 


Cooperative   Goal  Alining   Series 

BULLETIN  17 


SURFACE  SUBSIDENCE  IN  ILLINOIS 


RESULTING    FROM 


COAL  MINING 


BY 

LEWIS  E.  YOUNG 


ILLINOIS   COAL   MINING    INVESTIGATIONS 

( Prepared  under  a  cooperative  agreement  between  the   Illinois  State-  Geological  Suxv«  v. 

the  Kngineering  Experiment  Station  of  the  University  oi  Illinois,  and 

the  U.  S.  Bureau  of  Mines.) 


I'KINTKO    BY    AU'I  IIOKITY    OF   THE    STATE    OF    ILLINOIS 


ILLINOIS  STATE  GEOLOGICAL  SURVEY 

UNIVERSITY  OK  ILLINOIS 

URBANA 

L916 


CONTENTS 


PAGE 

Chapter  I — Introduction    11 

Area  investigated .  ,    11 

Scope  and  object  of  report , 11 

Acknowledgments    13 

Illinois  coal  field  and  production  data 15 

Chapter  II — Geologic  conditions  affecting  subsidence 18 

Description  of  Illinois   "Coal  Measures" 18 

Strata  associated  with  Illinois  coal  beds 21 

Cleat     26 

Faults  and  rolls 27 

General  relations  to  subsidence 27 

Coal  No.  2 27 

Coal  No.  5 27 

Coal  No.  6 28 

Coal  No.  7 29 

Chapter  III — Damage  caused  by  removal  of  coal 30 

Contrasting  effects  of  longwall  and  room-and-pillar  methods 30 

Surface  evidences  of  subsidence 30 

Surface   cracks   and   displacements 30 

Pit  holes  or  caves 34 

Sags    42 

Agriculture  and  surface  subsidence 50 

Importance   of  agriculture 50 

Extent  and  value  of  farm  lands 50 

Value  of  coal  lands 54 

Nature  of  damage  to  agricultural  lands 56 

Restoring  agricultural  lands 58 

Transportation  and  surface  subsidence 61 

Railroads    61 

Wagon  roads 64 

Streams   and    canals 64 

Buildings  and  improvements  affected  by  subsidence 65 

Buildings     65 

Streets,  pipe  lines,  and  sewers 69 

Water  supply 71 

Municipal   waterworks 71 

Reservations   of   coal 72 

Chapter  IV — Subsidence  data  by  districts 73 

Introductory    statement 73 

District    1 75 

District  II 78 

District  III 78 

District   IV 79 

District  V 81 

(5) 


PAGE 

District  VI 83 

District  VII 8S 

District   VIII 86 

Chapter  V— Protection   of   surface 88 

General   considerations °° 

Pillars    88 

Crushing  strength  of  coal °° 

Angle  of  break  and  angle  o  f  d raw °9 

Safe  depth   9 1 

Theory  as  previously  advanced 93 

Increase  in  volume  of  rock  by  breaking 93 

Compressibility  of  broken  rock 94 ! 

Shaft    pillars 10° 

Room  pillars 


Filling   methods. 


103 


Gobbing     103 

Hydraulic  filling 104 

Griffith's  method  of  filling 104' 

Artificial   supports ^5 

Chapter  VI— Investigations  of  subsidence 106 

European    10° 

United    States '. 106 

Suggested  Illinois  investigations 106 

Considerations     106 

Typical  mines 107 

Monuments  and  surveys 107 

Underground  work 107 

Possible  benefits 10° 


(6) 


ILLUSTRATIONS 

PLATE  PAGE 

I.     General  geological  sections  for  southwestern  Illinois 18 

II.     General  geological  sections  in  coal  field  of  Williamson  and  Franklin  counties     20 

III.  Graphic  sections  in  Longwall  District 22 

IV.  Cross-sections  CD  and  EF  showing  structure  across  the  southern  and  north- 

ern parts  of  the  Danville  field 24 

FIGURE 

1.  Map  of  Illinois  showing  extent  of  the  "Coal  Measures" 12 

2.  Map  of  Illinois  showing  distribution  of  thick,  medium,  and  thin  coal 14 

3.  Map  showing  area  underlain  by  principal  coal  seams 16 

4.  Graphic  section  showing  persistent  nature  of  limestones  in  the  McLeansboro 

formation     20 

5.  Diagrammatic  illustration  showing  angle  to  break  and  angle  of  subsidence.  ...  31 

6.  Crack  in  the  soil  caused  by  room-and-pillar  mining  at  Streator 32 

7.  Plan  of  two  panels  of  Franklin  County  mine  showing  relation  of  subsidence 

to  underground  workings 33 

8.  Crack  due  to  subsidence  over  north  panel  shown  in  figure  7 34 

9.  Cracks  due  to  subsidence  over  south  panel  shown  in  figure  7 35 

Cracks  and  breaks  due  to  shear 36 

Buckling  of  frozen  sod  due  to  compression  along  the  axis  of  a  sag 36 

Surface  breaks  in  a  field  near  Carterville 37 

Surface  breaks  over  a  mine  near  Harrisburg 37 

14.     Plan  showing  workings  of  a  mine  and  location  of  subsidence  movements  ad- 

j  acent  to  a  dike 38 

Plan  of  a  mine  showing  details  of  movement  near  a  dike IS 

Breaks  in  a  pasture  over  an  abandoned  mine  west  of  Danville 39 

Side-hill  breaks  near  Cuba  caused  by   room-and-pillar  mining 39 

Large  area  covered  by  pit  holes  in  the  suburbs  of  a  town  in  central  Illinois.  .  .  40 

Cave-in  south  of  Dewmaine 40 

Detail  of  a  cave  on  a  hillside  near  Streator 41 

|21.     Side-hill  breaks  over  shallow  workings  near  Streator 41 

22.  Plan  of  a  40-acre  tract  in  southern  Illinois  showing  relation  of  approximately 

60  pit  holes  to  underground  workings 42 

23.  Topographic  map  of  the  Coal  City-Wilmington  area 43 

24.  Pond  in  a  sag  due  to  longwall  mining  at  Coal  City 44 

25.  Plan  of  a  mine  in  Perry  County  showing  relation   of   sags  to  underground 

workings    45 

Telephone  poles  tipped  toward  a  sag  over  a  mine  in  Franklin  County 46 

Swamp  in  a  typical  sag  in  Randolph  County 47 

Pond  in  a  sag  near  Clifford,  Williamson  County 48 

Flooding  of  a  large  tract  due  to  subsidence  in  Franklin  County 48 

(7) 


FIGURE  PAGE 

30.  Pond  due  to  subsidence  at  Westville,  Vermilion  County 49 

31.  Open  space  in  a  cornfield  south  of  Danville 49 

32.  Drowned-out  area  of  corn  near  Nokomis 49 

33.  Map  showing  the  relation  of  different  thicknesses  of  coal  to  values  of  farm 

lands  in  1910 51 

34.  Map  showing  location  of  tile  drains  laid  by  a  mining  company  to  drain  sags.  .  58 

35.  Pit  hole  filled  with  rubbish  at  Electric  mine  near  Danville 59 

36.  Pit  holes  and  cracks  over  shallow  mine  near  Streator 60 

37.  Pit  holes  near  Streator  filled  with  mine  rock  and  soil 60 

38.  Railroad   track  in    Franklin   County   lowered   by   subsidence   over   room-and- 

pillar  mine 62 

39.  Plan  showing  relation  of  railroad  in  figure  38  to  mine  workings 63 

40.  Repaired  railroad  trestle  in  Franklin  County 64 

41.  House  near  Coal  City  lowered  9  inches  at  one  corner 65 

42.  Brick  house  near   Danville   abandoned  on   account  of  danger  by   room-and- 

pillar  mining 66 

43.  Plan  showing  relation  of  house  in  figure  42  to  the  pillar  in  the  mine 67 

44.  Houses  in  Springfield  for  which  claims  were  paid  by  a  mining  company 68 

45.  Small  house  near  Streator  beside  which  a  pit  hole  has  formed 68 

46.  Flooded  streets,  broken  sidewalks  and  foundations,  and  damages  to  plaster- 

ing resulting  from  subsidence  in  Franklin  County 69 

47.  Barn  of  mining  company  lowered  4  feet  at  one  end 69 

48.  Broken  sidewalk  caused  by  subsidence  in  Franklin  County 70 

49.  Map  showing  division  of  State  into  districts 74 

50.  Cracks  in  the  immediate  roof  of  a  longwall  mine  in  the  La  Salle  area 90 

51.  Stress  diagram  of  an  ideal  homogeneous  cantilever 91 

52.  Stress  diagram  of  a  low-down  neutral  surface 92 

53a.  Diagrammatic  illustration  through  the  gob  and  parallel  to  the  face  of  a  long- 
wall  mine 96 

b.  Plan  showing  pack  walls  and  loose  gob  between  roadways  and  cross  entries 

in  the  same  mine 96 

54.  Diagrammatic  illustration  showing  the  flow  of  roof  shale  under  pressure  in 

a  mine  near  Peoria 98 

55.  Diagrammatic  illustration  showing  the  size  of  shaft  pillars  for  given  depths 

as  recommended  by  various  mining  engineers 

56.  Diagrammatic   illustration   showing  the  extent   of  subsidence   resulting   from 

the  removal  of  adjacent  pillars 102 


99 


(8) 


TABLES 

PAGE 

1.  Output  of  Illinois  coal  by  coal  seams 15 

2.  Output  of  Illinois  coal  by  depth  of  shaft 17 

3.  Character  of  roof  and  floor  of  the  commercial  coal  beds  throughout  Illinois..  24 

4.  Value  of  farm  lands,  April  15,  1910 53 

5.  Value  of  surface  and  of  coal  rights  by  counties  in  Illinois 55 

6.  Assessed  value  of  coal  rights  and  of  agricultural  lands  by  counties 56 

7.  Districts  into  which  the  State  has  been  divided  for  the  purpose  of  investigation  73 

8.  Alphabetical  arrangement  of  coal-producing  counties 75 

9.  Longwall  mines  in  Illinois 76 

10.  Data  on  subsidence  in  District  IV 80 

11.  Data  on  subsidence  at  typical  mines  in  District  V 83 

12.  Data  on  subsidence  at  typical  mines  in  District  VI 84 

13.  Data  on  subsidence  at  typical  mines  in  District  VII 85 

14.  Compression  tests  of  Illinois  coals 89 

15.  Volumes  of  different  materials  after  crushing  as  compared  with  volumes  "in 

the   solid" 94 

16.  Compressibility  of  different  materials  after  having  been  crushed 94 

17.  Compressibilty  tests  upon  crushed  materials  made  by  the  United  States  Bureau 

of   Mines 95 


(9) 


SURFACE  SUBSIDENCE  IN  ILLINOIS 
RESULTING  FROM  COAL  MINING 

By  Lewis  E.  Young 


CHAPTER  I— INTRODUCTION 
Area  Investigated 

During  the  summer  of  1914  there  was  made  a  preliminary  study 
of  surface  subsidence  resulting  from  coal  mining  operations  in  Illinois. 
Mines  were  visited  in  24  of  the  52  counties  in  which  shipping  mines  are 
located.  These  24  counties  produced  94  per  cent  of  the  coal  mined 
in  the  State  in  1913.  Within  these  24  counties  are  324  of  the  371 
shipping  mines  listed  in  1913  and  293  of  the  469  local  mines.  The 
counties  visited  were  Bureau,  Christian,  Clinton,  Franklin,  Fulton, 
Grundy,  Jackson,  La  Salle,  Livingston,  Macon,  Macoupin,  Madison, 
Marion,  Montgomery,  Peoria,  Perry,  Randolph,  St.  Clair,  Saline,  San- 
gamon, Vermilion,  Washington,  Will,  and  Williamson.  In  all  but  three 
of  these  counties  coal  mining  has  resulted  in  subsidence  of  such  in- 
tensity as  to  result  in  substantial  damage  to  surface  property. 

Data  were  secured  from  108  companies  operating  149  separate 
plants,  and  in  addition,  the  field  notes  of  the  Cooperative  Investiga- 
tion upon  100  Illinois  mines  supplied  data  on  8  mines  not  visited  for 
this  particular  purpose. 

Scope  and  Object  of  Report 

Prior  to  this  preliminary  survey  no  work  upon  the  subsidence 
problem  in  Illinois  had  been  undertaken  by  any  scientific  bureau. 
For  over  a  quarter  of  a  century  there  has  been  litigation  between  the 
operators  of  coal  mines  and  the  owners  of  the  surface  when  surface 
subsidence  has  been  attributed  to  coal  mining  operations.  There  is  a 
need  for  more  definite  knowledge  concerning  (1)  the  extent  to  which 
the  complete  removal  of  coal  may  disturb  the  overlying  rock  strata, 
(2)  the  percentage  of  coal  that  may  be  mined  without  disturbing  the 
surface,  (3)  the  methods  of  mining  that  should  be  employed  in  order 
to  minimize  the  surface  movement  following  the  removal  of  the  coal, 

(4)  the  methods  of  protecting  the  surface  by  artificial  supports,  and 

(5)  the  best  methods  and  policies  to  be  employed  in  conserving  the 
mining  and  agricultural  resources  of  the  State. 

At  the  present  time  there  is  more  or  less  unrest  in  certain  coal 
mining  districts  in  Illinois  on  account  of  minor  damage  to  the  surface. 

(11) 


map  or 

ILLINOIS 


Fig.  1.— Map  of  Illinois  showing  extent  of  the  "Coal  Measures." 


INTRODUCTION  13 

At  a  number  of  points  mine  operators  are  being  forced  to  pay  claims 
for  damages  much  in  excess  of  the  actual  cost  of  restoring  the  injured 
property.  There  is  an  urgent  need  for  definite  data  upon  the  experience 
of  operators  in  the  various  districts,  so  that  those  who  mine  coal  in 
the  future  may  be  able  to  recover  the  maximum  percentage  of  the 
coal  with  the  least  damage  to  the  surface  or  with  the  briefest  inter- 
ference with  the  use  of  the  surface  property. 

It  is  undoubtedly  to  the  interest  of  the  State  to  conserve  the 
coal  supply  by  securing  as  complete  extraction  as  possible  from  the 
areas  in  which  mining  is  now  being  carried  on.  Almost  one-half  of 
the  coal  is  being  left  in  the  ground  and  made  unavailable  for  future 
mining,  and  in  some  places  a  large  part  of  this  abandoned  coal  is 
left  because  the  mine  operators  fear  that  by  removing  a  larger  per- 
centage they  may  cause  surface  subsidence  and  be  required  to  pay 
damages  out  of  proportion  to  the  real  value  of  the  surface.  In  many 
places  the  surface  may  be  restored  at  little  expense.  But  until  the 
prevailing  conditions  are  known  accurately  and  the  essential  facts  are 
understood  and  studied,  the  State  cannot  consider  or  propose  meas- 
ures to  relieve  the  mining  industry  of  this  severe  burden. 

With  these  problems  and  difficulties  in  view,  this  preliminary 
survey  was  made,  and  the  data  collected  show  in  an  impartial  manner 
the  situation  as  it  exists  in  Illinois  at  the  present  time. 

Acknowledgments 
The  writer  wishes  to  acknowledge  his  indebtedness  to  Mr.  G.  S. 
Rice,  Chief  Mining  Engineer,  U.  S.  Bureau  of  Mines ;  Professor  H.  H. 
Stoek,  head  of  the  Department  of  Mining  Engineering,  University  of 
Illinois;  and  Mr.  F.  W.  DeWolf,  Director  of  the  Illinois  State  Geo- 
logical Survey,  under  whose  combined  direction  the  work  of  the  in- 
vestigation has  been  carried  on.  Mr.  S.  (..).  Andros  of  the  De- 
partment of  Mining  Engineering,  University  of  Illinois,  lias  been 
very  helpful.  The  various  State  and  county  mine  inspectors 
have  been  uniformly  courteous  in  furnishing  much  useful  in- 
formation. Messrs.  II.  I.  Smith  and  J.  R.  Fleming,  Assistant  Min- 
ing Engineers,  U.  S.  Bureau  of  Mines,  have  made  valuable  suggestions 
and  have  furnished  numerous  photographs  for  which  acknowledg- 
ments are  made  in  proper  place.  Mr.  R.  Y.  Williams,  formerly  mining 
engineer,  U.  S.  Bureau  of  Mines,  furnished  much  of  the  data  on 
Saline  County.  To  the  following  representatives  of  the  coal  mining 
industry  in  Illinois  the  author  is  deeply  indebted  for  many  courtesies 
and  for  close  cooperation :  Mr.  W.  M.  Cole,  Mining  Engineer,  Spring 
Valley  Coal  Company;  Mr.  J.  Quaid,  General  Superintendent,  Big 
Creek  Coal  Company;  Mr.  C.  II.  Nicolet,  Engineer,  Matthiessen  and 
Hegeler  Coal  Company;  Mr.  R.  D.   Brown,  Chief  Engineer,  O'Gara 


Fig.  2. — Map  of  Illinois  showing  distribution  of  thick,  medium,  and  thin 
coal.     (After  Bement.) 


INTRODUCTION  15 

Coal  Company;  Mr.  R.  Williams,  Mining  Engineer,  Saline  County 
Coal  Company ;  Mr.  R.  Forrester,  Superintendent,  Paradise  Coal  Com- 
pany;  Mr.  A.  J.  Moorshead,  President,  Madison  Coal  Corporation; 
Mr.  G.  E.  Lyman,  Chief  Engineer,  Madison  Coal  Corporation;  Mr. 
John  P.  Reese,  Superintendent,  Superior  Coal  Company;  Mr.  S.  F. 
Jorgensen,  Chief  Engineer,  Superior  Coal  Company ;  Mr.  T.  P.  Brew- 
ster, General  Manager,  Mount  Olive  and  Staunton  Coal  Company; 
Mr.  James  Dubois,  Superintendent,  Dering  Coal  Company;  Mr. 
Thomas  Moses,  General  Superintendent,  Bunsen  Coal  Company;  Mr. 
M.  F.  Peltier,  Chief  Engineer,  Peabody  Coal  Company;  Mr.  J.  A. 
Garcia,  Mining  Engineer;  Mr.  D.  J.  Carroll,  Chicago,  Wilmington  & 
Franklin  Coal  Company. 

Illinois  Coal  Field  and  Production  Data 

Estimates  made  by  the  Illinois  State  Geological  Survey  show  that 
the  known  coal  areas  of  Illinois  contained  approximately  175,000,000,- 
000  tons  of  coal  in  beds  not  less  than  three  feet  in  thickness.  The 
coal-bearing  formations  underlie  part  or  all  of  86  counties,  an  area  of 
about  36,800  square  miles  (fig.  1).  It  may  be  noted  that  674  square 
miles  are  underlain  by  several  coal  beds  over  3  feet  thick  or  an  aggre- 
gate thickness  of  15  feet;  3,883  square  miles  are  underlain  with  an 
aggregate  thickness  of  11  feet;  12,546  square  miles  with  an  aggre- 
gate thickness  of  7  feet;  and  10,184  square  miles  with  3  feet  of  coal. 
Figure  2  shows  approximately  the  extent  of  the  thick,  medium,  and 
thin  coal;  and  figure  3  shows  the  area  underlain  by  the  principal  coal 
seams. 

Practically  the  entire  output  of  Illinois  coal  in  1913  was  pro- 
duced from  5  seams,  as  shown  in  the  accompanying  table.1 

Table  1. — Output  of  Illinois  coal  by  coal  scams 
(Year  ended  June  30,  1913) 

Tons 

Coal  No.  1   500,000 

Coal  No.  2  5,650,000 

Coal  No.  5  13,500,000 

Coal  No.  6  41,400  000 

Coal  No.  7  750,000 

Total  from  5  seams 61,800,000 


n^otal   for   the   State   as   given    by    Illinois   Coal   Report,    1913,   was   61,846,204    tons. 


Fig.  3.— Map  showing  area  underlain  by  principal  coal  seams.     (After  Bement.) 


INTRODUCTION  17 

The  greater  portion  of  the  output  comes  from  shafts  100  to  400 
feet  in  depth.    Table  2  shows  the  relation  of  tonnage  to  depth.1 

Table  2. — Output  of  Illinois  coal  by  depth  of  shaft 
(Year  ended  June  30,  1913) 

shaft                                  Number  of  shafts  Output 

Tons 

489    6,500,000 

159     17,400,000 

73    11,500,000 

46    11,500,000 

33    8,750,000 

18    2,750,000 

12    2,350,000 

6    720,000 

2    180,000 

1     105,000 

1     75,000 


Depth 

of 

Feet 

0- 

99 

100- 

199 

200- 

299 

300- 

399 

400- 

499 

500- 

599 

600- 

699 

700- 

799 

800- 

899 

900- 

999 

1,000-1,099 

Total    61,830,000 


CHAPTER  II— GEOLOGICAL  CONDITIONS  AFFECTING 
SUBSIDENCE 

It  is  evident  that  whatever  movement  may  result  from  under- 
ground mining  will  be  influenced  greatly  by  the  nature  of  the  rock  over- 
lying the  coal  seam  being  worked.  As  noted  in  Table  2,  the  greater 
part  of  the  output  of  Illinois  coal  is  from  shafts  not  exceeding  400 
feet  in  depth,  and  practically  50  per  cent  of  the  output  is  from  shafts 
not  over  300  feet  deep.  Throughout  the  greater  part  of  the  State  the 
coal  beds  lie  practically  flat. 

Description  of  Illinois  "Coal  Measures" 

The  following  extracts1  give  a  concise  statement  of  the  essential 
facts  concerning  the  coal-bearing  formations.  Plate  I  shows  general 
geological  sections  for  southwestern  Illinois,  Plate  II  shows  sections  in 
the  Williamson-Franklin  field,  Plate  III  shows  sections  in  the  coal 
fields  of  northern  Illinois,  and  Plate  IV  shows  sections  in  the  Dan- 
ville field. 

The  coals  of  Illinois  exist  as  widespread  beds  or  as  local  pockets  among 
layers  of  shale,  sandstone,  and  limestone  which  together  make  up  the  Pennsyl- 
vanian  series.  There  are  five  coals  known  to  be  important  enough  to  have 
special  names,  and  numerous  other  beds  occur  at  various  depths.  The  maximum 
thickness  of  Pennsylvanian  rocks  is  known  to  be  at  least  2,200  feet,  though  it  is 
not  to  be  assumed  that  a  single  bore  hole  could  penetrate  all  of  the  various  forma- 
tions at  the  place  of  extreme  thickness. 

The  Pennsylvanian  series  has  been  divided  for  convenience  of  description 
into  three  formations  which  present  different  characteristics  as  to  time  of  deposi- 
tion, physical  composition,  and  economic  importance.  The  divisions  from  the 
bottom  upwards  are  the  Pottsville,  Carbondale,   and  McLeansboro   formations. 


POTTSVILLE   FORMATION 

The  lowermost  formation  of  the  Pennsylvanian  in  Illinois  is  composed 
chiefly  of  massive  sandstones  interrupted  by  thinner  beds  of  shale  and  beds  or 
pockets  of  coal  and  fire  clay. 

In  Illinois  this  formation  carries  plant  fragments  which  indicate,  according 
to  White,"  that  deposition  took  place  during  late  Pottsville  time  of  the  Appala- 
chian coal  basins.  The  early  sediments  are  thinner  to  the  north  and  west  and 
are  nearly  or  quite  absent  over  much  of  the  State.  Massive  sandstones  in  the 
Rock  Island  region  are  of  Pottsville  age,  but  later  than  the  first  sediments 
of  southern  Illinois.  There  are  a  number  of  occurrences  of  coal  in  the  Pottsville 
in  southern  counties  but  at  present  they  have  no  commercial  importance,  because 


Preliminary  report  on  organization  and  method  of  investigations,  Illinois  Coal  Mining 
Investigations,   pp.    48-51,    1913. 

2White,   David,   111.   State   Geol.   Survey   Bull.    14,   p.    293,   1908. 

(18) 


KM 


19 


ooa 


008 


ILLINOIS   STATU  GEOLOGICAL   SURVEY 


COOPERATIVE  COAL  MINING  SERIES 
BULLETIN  17,  PLATE  I 


I  £         f> 


\^_Z:\  Lime  Shells 

P=l  Shel. 

WJM  "«<i  Shale 

'    [  Sandstone 

\~— Zir\  Surface  or  Orllt 

|  ',  -.|  Gravel  or  Bouldei 

r'VT'f 


\  W 


RELATIONS    OF  ( 


SOUTHWEST! 


-BEARING  R< 
*N   ILLINOIS 


K.I 


k*  r 

— LA— i 

r        \  V-- 


CONDITIONS    AFFECTING    SUBSIDENCE  19 

of  local  or  pockety  character.  Coal  of  No.  1  of  Rock  Island  and  Mercer  counties 
is  similarly  restricted  in  area  but  is  thick  enough  to  be  valuable.  The  topmost 
sediments  of  the  Pottsville  in  Illinois  include  the  Cheltenham  fire  clays,  which 
have  been  traced  through  the  counties  between  St.  Louis  and  Rock  Island,  and 
thence  eastward  to  Ottawa.  The  Pottsville  closed  just  before  the  deposition  of 
coal  No.  2.     (Murphysboro,  La  Salle,  Third  Vein,  etc.) 

CARBONDALE    FORMATION 

The  second  division  of  the  Pennsylvanian  series  extends  from  the  base  of 
coal  No.  2  up  to  the  top  of  coal  No.  6.  (Herrin,  Belleville,  Blue  band,  etc.). 
It  represents  a  time  interval  comparable  to  the  Allegheny  formation  of  the  eastern 
states,  though  the  close  of  Allegheny  time  in  Illinois  has  not  been  definitely  deter- 
mined and  may  include  some  of  the  strata  lying  above  the  Carbondale  as  here 
defined. 

The  Carbondale  is  composed  chiefly  of  shale  and  lesser  amounts  of  sand- 
stone, coal,  and  limestone.  It  includes  all  the  coals  mined  for  commercial  ship- 
ment except  the  Rock  Island  (No.  1)  bed,  and  the  Danville  (No.  7)  bed.  This 
formation  extends  over  practically  the  whole  coal-area,  but  its  upper  beds  are 
absent  along  the  rim  and  its  lower  beds  are  not  well  known  in  the  central  part 
of  the  basin.  The  thickness  varies  considerably,  being  from  200  to  240  feet  in 
the  La  Salle  region,  200  feet  at  Peoria,  300  feet  at  Mattoon,  and  285  feet  or  more 
in  the  southern  counties  of  the  coal  field. 

MCLEANSBORO   FORMATION 

The  topmost  division  begins  at  the  top  of  coal  No.  6  and  extends  up  to 
the  highest  Pennsylvanian  rocks  of  the  State  (fig.  4).  With  the  exception 
of  the  Danville  coal  (No.  7)  which  at  present  is  included  in  this  formation, 
there  are  no  coals  of  known  importance,  although  a  thin  bed  in  Shelby  County 
is  mined  for  local  use.  The  formation  is  dominated  by  beds  of  shale  and  sand- 
stone, among  which  are  found  some  thin  limestones.  The  Carlinville  (Shoal 
Creek)  limestone  occurs  about  275  feet  above  the  base  of  the  formation  and  is 
persistent  over  a  considerable  area.  The  greatest  thickness  of  the  formation 
seems  to  be  in  the  vicinity  of  Hamilton  and  White  counties  where  coal  No.  6  lies 
approximately  1000  feet  below  the  surface.  A  somewhat  less  reliable  record  at 
Olney  indicates  a  depth  of  1155  feet  for  this  coal. 

SPOON-SHAPED    STRUCTURAL   BASIN 

The  strata  beneath  the  surface  deposits  of  Illinois  to  a  great  extent  lie 
horizontal,  but  locally  dip  as  much  as  350  feet  to  the  mile.  When  all  the  evi- 
dence from  mine  shafts  and  bore  holes  is  studied  it  is  evident  that  the  State  is 
an  immense  spoon-shaped  basin  with  the  tip  in  the  extreme  northwest  counties 
and  the  bowl  in  the  region  of  Wayne,  Edwards,  Hamilton,  and  White  counties. 
The  long  axis  of  the  "spoon"  passes  near  Olney  in  Richland  County  and  Loving- 
ton  in  Moultrie  County,  and  the  dip  in  the  central  part  of  the  basin  towards  this 
axis  is  commonly  as  low  as  10  feet  per  mile. 

Thus,  an  east-west  section  from  Springfield  eastward  to  Cerro  Gordo  in 
Piatt  County  has  a  dip  of  300  feet  in  50  miles  or  6  feet  per  mile.  Similiarly, 
the  dip  eastward  from  Iuka  in  Marion  County  to  Olney  in  Richland  County  is 
400  feet  in  40  miles  or  10  feet  per  mile. 


20 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


The  warping  of  the  strata  along  the  southwestern  and  southern  rim  of 
the  basin  has  been  much  more  pronounced  and  has  been  somewhat  relieved  by 
the  Shawneetown  fault,  which  extends  as  a  narrow  belt  from  western  Kentucky 
into  Illinois  at  Shawneetown  and  has  been  traced  at  least  15  miles  farther  west. 
This  fault  causes  the  strata  on  the  north  to  be  about  1400  feet  lower  than  those 
on  the  south.  North  of  the  fault  and  along  the  border  of  the  active  coal  field, 
the  dip  from  Cottage  Grove  in  Saline  County  northward  to  Eldorado  averages 
115  feet  per  mile.  Similarly  from  Marion  northward  to  West  Frankfort  it  aver- 
ages 50  feet  per  mile  and  locally  is  double  this  amount.     In  the  hills  5  miles 


New  Haven 


Shoal  Creek 


Coal  No.8 


Coal  No.7 
|g    Top 


Shoal  Creek 


Coal  No.8 


Coal  No.7 
Coal 


New  Haven 


Shoal  Creek 


Coal  No.8 


Coal  No.7 


Shoal  Creek 


700 


600 


600 


300 


30   |s^t  Coal  No.7 
6 


■pic  4.— Graphic  sections  showing  persistent  nature  of  limestones  in  the  Mc- 
Leansboro  formation. 


northwest  of  Murphysboro  the  dip  is  eastward  at  a  rate  of  350  feet  per  mile. 
The  same  pitch  exists  also  in  the  area  one  mile  east  of  Duquoin. 

Although  the  Illinois  basin  is  approximately  spoon  shaped,  there  are  minor 
folds  and  terrace-like  flats  on  the  flanks.  The  most  notable  is  the  La  Salle  anti- 
cline, which  is  pronounced  at  La  Salle  and  also  in  the  oil  fields  of  Clark,  Craw- 
ford, and  Lawrence  counties.  Doubtless  it  extends  as  a  persistent  feature  with 
a  rather  uniform  direction  between  these  distant  areas.     The  west  side,  facing 


OCX 


21 


ooe 


oo* 


S 


>J8 

>ia 

>ia 


cos 


oo  r  j 


e 


N  ■  ■  m 


ounced 
to  Du- 
ti  anti- 
ase  the 
:d  have 
letailed 

vorable 
border 

:xtreme 
band) 

already 


ata  of 

>ortant 

iidence 

nation, 

)w  this 

Sm 

largely 

YTHUl 

No.  2 
etween 
not  as 

a  r.p 

:    ■ 

tion  in 

e  sand- 
)0  feet. 

.3  e.a 
.3  r  n 

shown, 
[ackson 
40  feet 

5  to  45 

een  de- 

ed as  a 

'erlying 

i   which 

beds  of 

r  inter- 

Bulletins 

aro-Herrin 

ILLINOIS  STATE  GEOLOGICAL  SURVEY 


COOPERATIVE  COAL  MINING  SERIES 
BULLETIN  NO.  17,  PLATE  II 


1 

Bk 

■v. 
Bk 

Bk 
N 

1 

Wi 

%- 

1 

J 

82          Base 

& 

-6 

~5  — —  - 

-7-_ 

Jr*"" 
16-- 
"16 

103        of 

-at 

Bk 

Bk 
Bk 

Bk  - 

£=^ 

Pi 

~ 

""-— 

r:;1'- 

':-     : 

""     : 

Prll 

:w_ 

-■ 

--::- 

SB 

W 

^~, , 

ri 

— 

- 

( 

~i 

]Pi 

Bk 
Bk 

- 

Bk 

»— 

HI 

< 

H 

44  Coal  Nb.5 

10 
14 

LEGEND 
1  I  '  I  1  Limestone 
E=dEJ|  Shale 
|.';'.;';-;'|  Sandstone 
IV^rj  Drift 
|iS^   Coal 
^ggj  Fire  clay 
^=±t|  Calcareous  s 

:r- 

■"->- 

_- 

ale 

^ 

Bk 
No.6      Bk 


JEFFERSON   COUNTY 

1  Sec.  24.  T.  2  S..R.  1  E. 

2  Sec.  30,  T.  4  S..R.2  E. 

SHELBY    COUNTY 

3  Sec.  8,  T.  10  S..R.  1   E. 

FRANKLIN    COUNTY 

4  Sec.  35,  T.  5  S.,R.  4.  E. 

5  Sec.  19.T.6  S..R.3  E. 

6  Sec.  32.  T.  7  S..R.  1   E. 


FEET 
800 


S 


91 

54  Coal  No.5 


Graphic  sections  of  borings  showing  the  general  character  of  the  McLeansboro  formation  in  District  VI  and  Shelby  County 


CONDITIONS    AFFECTING    SUBSIDENCE  21 

the  axis  of  the  basin,  is  much  steeper  than  the  east  flank.  Another  pronounced 
anticline  has  been  traced  from  the  region  5  miles  west  of  Murphysboro  to  Du- 
quoin  and  thence  northward  to  Centralia  and  Sandoval.  This  Duquoin  anti- 
cline is  also  steeper  on  the  side  facing  the  axis  of  the  basin,  in  this  case  the 
east  side.  Folds  and  faults  of  appreciable  size  other  than  those  mentioned  have 
been  discovered,  and  doubtless  they  will  be  found  to  be  numerous,  as  detailed 
surveys  proceed. 

The  structural  relations  in  Illinois  are  on  the  whole  unusually  favorable 
to  coal  mining.  The  first  effect  is  of  course  to  make  the  coal  around  the  border 
of  the  field  more  easily  available  than  that  in  the  deeper  portion,  but  the  extreme 
depth  necessary  to  reach  the  most  important  coal  (No.  6,  Herrin,  Blue  band) 
probably  will  not  greatly  exceed  1000  feet,  and  the  shaft  at  Assumption  is  already 
operating  successfully  to  approximately  this  depth. 

Strata  Associated  with  Illinois  Coal  Beds 

It  is  important  that  attention  be  directed  to  the  thick  strata  of 
limestone,  shale,  and  sandstone,  which  lie  above  the  various  important 
coal  seams,  as  these  may  affect  the  rate  and  amount  of  subsidence 
when  underlying  seams  are  mined.3 

As  previously  noted  coal  No.  1  lies  in  the  Pottsville  formation, 
but  the  important  beds  of  sandstone  and  of  conglomerate  lie  below  this 
seam.  The  Illinois  strata  in  the  Pottsville  above  this  seam  are  largely 
fire  clays  and  shales. 

The  Carbondale  formation  extends  from  the  base  of  coal  No.  2 
to  the  top  of  coal  No.  6.  In  northern  Illinois  the  boundary  between 
the  Carbondale  and  the  overlying  McLeansboro  formation  is  not  as 
clearly  marked  as  in  southern  Illinois.  The  Carbondale  formation  in 
southern  Illinois  is  composed  chiefly  of  shale  but  includes  some  sand- 
stones and  limestones.  The  thickness  varies  from  200  to  300  feet. 
In  several  typical  bore  holes,  both  limestones  and  sandstones  are  shown, 
but  the  thickest  single  beds  of  each  are  about  8  feet.  In  Jackson 
County,  however,  the  Vergennes  sandstone  lies  from  20  to  40  feet 
above  coal  No.  2.  This  is  persistent  but  irregular  in  thickness  (15  to  45 
feet)  and  varies  from  a  sandstone  to  a  sandy  shale.  It  has  been  de- 
scribed as  micaceous,  loose,  and  friable  and  can  not  be  regarded  as  a 
bed  that  will  be  strong  enough  to  check  subsidence  of  the  overlying 
beds.4 

Overlying  coal  No.  6  is  the  McLeansboro  formation  in  which 
only  coal  No.  7  is  of  commercial  importance.  The  following  beds  of 
this  formation  are  reasonably  persistent,  whereas  some  of  their  inter- 
vening beds  vary  greatly  in  character. 


8For  detailed  reports  on  the  geology  of  the  districts  see  the  Cooperative  Bulletins 
Nos.    10,    11,    14,   and    15. 

4Shaw,  E.  W.  and  Savage,  T.  E.,  U.  S.  Geol.  Survey  Geol.  Atlas  Murphyshoro-Herrin 
folio    (No.    185),   p.    7,    1912. 


22  SURFACE    SUBSIDENCE   IN    ILLINOIS 

The  well-marked  lithologic  units  of  the  McLeansboro  (in  District 
VII)  may  be  enumerated  as  follows5 : 

5.  New  Haven  limestone,  200  to  250  feet  above  Carlinville  limestone 
(thickness  about  25  feet). 

4.  Shoal  Creek  limestone,  about  100  feet  above  the  Carlinville  (thick- 
ness 12  to  25  feet). 

3.  Carlinville  limestone,  from  200  feet  to  a  little  more  than  300  feet 
above  coal  No.  6  (average  thickness  7  feet). 

2.  A  bed  of  pink,  red,  or  variegated  shale,  variable  in  thickness,  aver- 
aging 35  to  50  feet  above  coal  No.  6  (seldom  exceeds  15  feet 
in  thickness). 

1.  A  hard  limestone  overlying  or  slightly  above  coal  No.  6  (averages 
7  feet  in  thickness). 

The  New  Haven  limestone  is  quite  persistent,  as  indicated  graph  - 
ically  in  the  records  from  Moultrie,  Shelby,  Montgomery,  and  Fayette 
counties  in  District  VII.  Mr.  G.  H.  Cady  reports  it  is  present  over 
parts  of  Franklin  County  from  500  to  550  feet  above  coal  No.  6. 
It  is  a  solid  bed  given  in  most  logs  as  25  feet  thick. 

The  Shoal  Creek  limestone  is  from  12  to  25  feet  thick  and  lies  275 
to  350  feet  above  coal  No.  6  in  District  VII.  It  is  described  as  lacking 
the  homogeneity  of  the  Carlinville  and  in  places  consists  of  a  series  of 
more  or  less  argillaceous  limestone  layers.6  This  limestone  apparently 
does  not  occur  continuously  over  District  VI. 

"The  Carlinville  limestone  is  one  of  the  most  widely  distributed 
in  the  'Coal  Measures'  of  Illinois.  It  has  been  traced  from  north  of 
Carlinville,  Macoupin  County,  southeast  to  the  Indiana  line  in  Gallatin 
County.  In  the  type  localities  this  limestone  is,  according  to  Udden, 
'generally  bluish  gray,  compact,  close  textured,  and  very  hard,  break- 
ing into  irregular,  splintery  pieces.  It  averages  about  seven  feet  in 
thickness'.  In  most  of  District  VII  the  interval  between  this  limestone 
and  coal  No.  6  averages  from  275  to  325  feet."7  In  District  VI  this 
stratum  occurs  from  250  to  300  feet  above  coal  No.  6  but  is  thin  and 
has  not  been  mentioned  in  many  of  the  records.8 

In  parts  of  Saline  and  Gallatin  counties  there  occurs  a  hard  sand- 
stone, known  locally  as  "Anvil  Rock",  a  sandstone  about  10  feet  above 
coal  No.  6.     In  several  of  the  small  mines  on  coal  No.  6  in  Gallatin 


5Kay,  Fred  H.,  Coal  resources  of  District  VII:  111.  Coal  Mining  Investigations  Bull. 
11,  p.  23,   1915. 

6Lee,  Wallace,  acknowledgements  to,  Illinois  Coal  Mining  Investigatons  Bull.  11, 
p.    26,    1915. 

7Kay,  Fred  H.,  Coal  resources  of  District  VII:  111.  Coal  Mining  Investigations  Bull. 
11,  p.   25,   1915. 

8Cady,  G.  H.,  Coal  resources  of  District  VI:  HI.  Coal  Mining  Investigations  Bull.  15, 
p.    34,    1916. 


1 

a 

t 

y 

n 

e 

il 

iS 

ie 
le 

s- 

a 

le 

iy 

6 

fr- 

ill 

c- 

7. 

:et 

lie 

ry 

nd 

lis 

lb 

id. 

b 

nil. 

ull. 

10, 

!ull. 

11  1  INOIS  STATE  GEOLOGICAL  SURVEY 


COOPERATIVE  COAL  MINING  SERIES 
BULLETIN  NO.  17.  TLATE  III 


13 


10 


6 

McLeansboro  <! 


#. 


I     Pottsvill 


=!S  i  Niagara 
wee  I 


I 


Lower     Magneslan  pr-r; 


LEGEND 


ESI 


E23 


E3 


_°z 


,£00/  _JVo._7 
Coal     .Yo.   B 


LEGEND 

ROCK 


111      ll 


E3 


E=l 


Fireclay 


Sandy 
shale 


ES 


Graphic  sections  in  the  Longwall  District.     Scale :  1  inch  equals  200  feet 


3 


CONDITIONS    AFFECTING    SUBSIDENCE 


23 


County,  it  serves  as  the  immediate  roof.  There  the  limestone  lying 
above  coal  No.  6  is  described  as  the  limestone  cap  rock.  Throughout 
District  VII  this  limestone  is  generally  not  less  than  2  feet  thick, 
although  in  several  small  areas  it  is  entirely  missing.  The  range  com- 
monly is  from  5  to  10  feet.  In  some  places  the  cap  rock  is  underlain 
by  black  "slate"  or  shale  a  few  feet  in  thickness,  and  in  others  by  a 
gray  shale  known  as  "white  top."9 

In  District  VI  the  cap  rock  occurs  over  a  large  part  of  the  district 
within  25  feet  above  coal  No.  6.  It  is  described  as  a  compact,  heavy- 
bedded  limestone,  commonly  dark  or  almost  black  when  fresh.  It  may 
be  as  thick  as  11  feet,  but  averages  4  or  5  feet.  Over  the  western 
part  of  District  VI  the  cap  rock  is  missing,  or  is  at  a  greater  distance 
above  the  coal.10 

A  log  given  as  typical  of  the  eastern  part  of  District  VII  shows, 
in  a  total  depth  of  658  feet  6  inches  to  the  top  of  coal  No.  6,  a  total 
thickness  of  24  feet  of  limestone  and  15  feet  of  sandstone. 

In  the  Longwall  District  the  strata  of  the  Pennsylvanian  series 
are  not  so  persistent  as  in  southern  Illinois.  Graphic  sections  in  the 
Longwall  District  are  shown  on  Plate  III.  So  far  as  is  known  no 
single  limestone  stratum,  except  the  Lonsdale  limestone,  is  traceable 
from  one  point  to  another  in  the  Longwall  District,  and  even  the  Lons- 
dale limestone  is  not  readily  identified  in  drill  records.  It  contains  a 
large  amount  of  argillaceous  material  and  is  easily  mistaken  for  shale 
in  drilling.11  "The  lower  5  feet. consists  of  a  firmly  cemented,  largely 
organic  limestone  in  beds  varying  in  thickness  from  6  inches  to  1  foot  6 
inches.  Above  these  firm  beds  there  are  15  feet  of  a  slightly  argilla- 
ceous and  more  flaggy  rock,  in  which  concretionary  structures  can 
nearly  always  be  detected."12  It  occurs  near  the  base  of  the  upper  sec- 
tion of  the  McLeansboro  formation  and  50  to  75  feet  above  coal  No.  7. 

In  the  upper  section  of  the  McLeansboro  and  about  400  feet 
above  coal  No.  2  or  175  feet  above  coal  No.  7  occurs  the  La  Salle 
limestone,  varying  from  25  to  30  feet  in  thickness.  "It  has  a  very 
local  distribution,  being  confined  to  a  belt  about  two  miles  broad  and 
extending  parallel  to  its  outcrop  along  the  anticline  from  Bailey  Falls 
on  the  south  to  the  NE.  yA  sec.  28,  T.  34  N.,  R.  1  E.,  three  miles  north 
of  La  Salle.    The  belt  is  much  wider  in  the  middle  than  at  either  q\\(\. 


"Kay,  Fred  H.,  Coal  resources  of  District  VII:  111.  Coal  Mining  Investigations  Bull. 
11,  p.   24,    1915. 

10Cady,  G.  II.,  Coal  resources  of  District  VI:  111.  Coal  Mining  Investigations  Bull. 
15,   p.    30,    1916. 

"Carly,  G.  H.,  Coal  resources  of  District  I:  111.  Coal  Mining  Investigations  Bull.  10, 
p.   41,    1915. 

"Udden,  J.  A.,  Geology  of  the  Peoria  quadrangle,  Illinois:  U.  S.  Geol.  Survey  Bull. 
506,  p.   39,  1912. 


24 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


The  same  horizon  extends  farther  westward,  but  the  lithological  change 
is  considerable.13  The  extent  to  which  these  beds  affect  subsidence 
in  the  Longwall  District  has  not  been  determined. 

From  the  foregoing  it  seems  that  there  are  few,  if  any,  persistent 
beds  that  are  hard  enough  and  thick  enough  over  large  areas  to  in- 
fluence greatly  the  problem  of  subsidence. 

By  the  Cooperative  Coal  Mining  Investigations  the  State  has 
been  divided  into  districts  as  shown  in  figure  49.  In  the  following 
tabulation  of  notes  on  roof  and  floor,  the  data  submitted  in  the  reports 
upon  the  several  districts  are  used  together  with  such  supplemental 
data  as  have  been  secured  later. 

Table   3. — Character   of  roof  and  floor   of  the   commercial  coal  beds 
throughout  Illinois 

Coal  No.  1 


Districts  and 
counties 

Roof 

Floor 

III 

In    Mercer    and    Rock    Island 
counties,  hard  black  shale  2  to 
5   inches   thick;   limestone    cap 
rock,  1  to  4  feet. 

Light  gray  micaceous  fire  clay 
which  heaves  badly  when  wet. 
In  places  an  irregular  band  (3 
to  6   inches)    of  carbonaceous 
shale  or  sandstone  lies  imme- 
diately below  the  coal. 

Coal  No.  2 


II 


III 


Gray  shale,  replaced  in  places 
by  a  black  shale  about  3  feet 
thick. 


Gray  shale  up  to  36  feet  thick. 
In  some  places,  dark-colored 
shale  which  is  hard  to  support. 

Hard  black  shale  generally  not 
over  1  foot  thick,  overlain  by 
a  limestone  cap  rock  3  feet 
thick. 


Dark-gray  fire  clay  up  to  sev- 
eral feet  thick.  In  some  parts 
of  the  La  Salle  field  a  hard 
sandstone  lies  directly  beneath 
the  coal. 

Bottom  bench  of  coal  is  a  layer 
of  bone  2  to  3  inches  thick.  In 
most  places  floor  is  sandstone; 
in  sections  is  shale  or  fire  clay. 

Gray  fire  clay  containing  nod- 
ules of  iron  pyrites. 


13Cady,  G.  H.,  Coal  resources  of  District  I:  111.   Coal  Mining  Investigations  Bull.   10, 

PP.    36-39,   1915. 


25 


I 


I 

S 

.w  sr  fl 

w  sr.fl,.n  i 

■ 

S 

st  thick, 
me     o  r 


[n   some 
idy    and 


eet  thick 
mestone. 
nines. 


eet  thick 
le.  The 
i    several 


t  in  most 


t    1    foot, 
re  is  gen- 


ILLINOIS  STATE  GEOLOGICAL  SURVEY 


COOPERATIVE  COAL  MINING  SERIES 
BULLETIN  NO.  17,  PLATE  IV 


1  Sec.12.T17  N..R.13W 

2  Sec.8.T17  N..R.12  W. 

3  Sec.4,T17  N..R.12  W. 

4  Sec.34.T.18  N..R.12  W 

5  Sec.36.T18  N..R.12  W. 

6  Sec.35.T.18  N..R.12  W 

7  Sec36.T18  N..R.12  W. 


8  Sec.36,T  18N..R.12  W. 

9  Sec.30,T  18N..R.11  W. 

10  Sec.29,T18N.,R.11  W. 

11  Sec.28,T.18N.,R.11  W. 

12  Sec.22.T18  N..R.11  W. 

13  Sec.24,T18  N..R.11  W. 


Columnar  Section  E  F 

1 

Sec.31,T.20  N..R.12  W. 

8     Sec.29,T.20N.,R.11  W. 

2 

Seo.32,T.20  N..R.12  W. 

9     Sec.21,T.20  N..R.11  W. 

3 

Sec.32,T.20  N..R.12  W. 

10  Sec.22,T.20  N.R.11  W 

4 

Sec.33,T.20  N..R.12  W. 

11  Seo.14,T.20  N..R.11  W. 

5 

Sec.34,T.20  N..R.12  W. 

6 

Sec.35,T.20  N..R.12  W. 

7 

Sec.36,T.20  N..R.12  W. 

(£3 Dri,t 

Hfl  Shale  gg]  Black  slate 

[H  Clod  §jjjj  Coal 

l-'y'vl  Sand  or  sandstone  |^OJ  Fire  clay 
|PEk]  Sand  and  shale 


Cross-section  CD  showing  structure  across  the  southern  part  of  the  Danville  field 
Cross-section  EF  showing  structure  across  the  northern  part  of  the  Danville  field 


CONDITIONS    AFFECTING    SUBSIDENCE 


25 


Coal  No.  5 


Districts  and 
counties 


Roof 


Floor 


IV 


Gray  fire  clay  1  to  4  feet  thick, 
underlain  b  y  sandstone  o  r 
sandy  shale. 


Varies  from  a  gray  shale  to 
black  "slate",  sandstone  and  lo- 
cally limestone;  "white  top" 
roof  in  certain  areas. 

Black  sheety  shale  up  to  35 
feet  thick.  A  limestone  cap 
rock  over  the  shale.  Where 
shale  is  thin,  the  cap  rock  be- 
comes the  roof. 

Light   gray   to    black   shale,   in    Fire   clay   generally.     In   some 


Gray  fire  clay. 


some  areas  laminated  with  coal 
for  a  distance  of  3  feet  above 
seam.  Shale  of  immediate  roof 
is  weak. 


areas    the    clay    is    sandy    and 
heaves  badly  when  wet. 


Coal  No.  6 


VI 

Franklin 


Williamson 


VII 

Clinton 


Christian 

Macoupin 
Madison 


Coal  is  left  as  immediate  roof. 
Upon  the  coal  is  a  thin  bed  of 
draw  slate,  and  within  25  feet 
above  the  coal  is  usually  a  lime- 
stone cap  rock  4  to  10  feet 
thick. 

Coal  is  left  generally  as  roof. 
In  a  number  of  mines  the  lime- 
stone cap  rock  is  missing  or 
higher  than  in  Franklin  County. 

Limestone  cap  rock,  5  to  15 
feet  thick.  In  places  black 
shale  between  limestone  and 
coal. 

Black  shale  overlain  by  lime- 
stone ranging  from  1  to  20  feet. 
In  some  mines  shale  between 
coal  and  limestone. 

Black  shale  with  limestone  cap 
rock. 

Gray  or  black  shale  of  varying 
thickness  overlain  by  limestone 
ranging  in  thickness  from  a 
few  feet  to  as  much  as  30  feet. 
In  some  places  limestone  rests 
on  the  coal. 


Gray  fire  clay  2  to  8  feet  thick 
underlain  by  a  sandy  limestone. 
Heaves  in  only  a  few  mines. 


Gray  fire  clay  2  to  4  feet  thick 
underlain  by  limestone.  The 
floor  heaves  badly  in  several 
mines. 

Clay,  18  inches  to  8  feet  in  most 
places  on  shale. 


Clay  of  variable  thickness. 


Clay  averaging  about  1  foot. 
Beneath  the  clay  there  is  gen- 
erally limestone. 


26 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


Table  3. — Character  of  roof  and  floor  of  the  commercial  coal  beds 

throughout  Illinois — Concluded 

Coal  No.  6 — Concluded 


Districts  and 
counties 

Roof 

Floor 

Marion 

Limestone   cap   rock,   about   15 
feet  thick. 

Clay  of  varying  thickness. 

Montgomery 

Limestone  cap  rock. 

Clay  of  variable  thickness. 

St.   Clair 

Black  shale  and  limestone. 

Thin  clay  on  limestone. 

Perry, 

Randolph,  and 

Washington 

Black  shale  under  limestone  to 
the  west  of  Duquoin  anticline. 
To  the  east,  the  same  limestone 
is  100  feet  above  coal. 

Clay  of  variable  thickness. 

Shelby  and 
Moultrie 

Shale  and  limestone. 

Shale,  clay,  limestone. 

Sangamon 

Irregular  shale   and  limestone. 

Thin  clay. 

VIII 

Roof    is    variable.      Immediate 
roof  generally  a  grayish-black 
shale  about  6  feet  thick.     Diffi- 

Generally a  grayish  fire  clay 
varying  in  thickness  up  to  sev- 
eral feet.     Heaves  badly  when 

cult  to  support  in  many  areas. 
Many  irregularities. 

wet.  A  bed  of  limestone  be- 
neath the  fire  clay. 

Coal  No.  7 


VIII 


Gray  silicious  shale  35  or  more 
feet  thick.  Immediate  roof  is 
generally  darker  than  the  upper 
beds  of  shale. 

Black  shale  up  to  several  feet 
thick  under  a  gray  shale  as 
much  as  50  feet  thick  in  places. 


Gray  fire  clay  2  to  3  feet  thick 
lying  on  sandstone.  Black  shale 
in  places  forms  the  floor. 


Immediate  floor  is  a  thin  bed 
of  clay  which  heaves  badly.  Be- 
neath is  a  layer  of  harder  clay 
5  to  15  feet  thick.  Some  streaks 
of  coal  in  the  clay. 


Cleat 

It  has  been  suggested  by  some  mine  operators  that  subsidence 
may  be  avoided  if  in  room-and-pillar  mines  the  rooms  are  driven  face 
on  the  cleat.  The  theory  is  that  the  immediate  roof  and  the  overlying 
strata  are  jointed  in  the  same  direction  as  the  cleat,  and  that  most  of 
the  slips  occurring  in  the  roof  also  run  in  the  direction  of  the  cleat.  It 
is  held  that  if  the  rooms  are  properly  turned,  the  pillars  will  catch  up 
these  slips  and  prevent  any  local  movement  which  may  be  the  beginning 
of  a  general  movement  causing  subsidence. 

At  the  present  time  there  are  not  sufficient  data  collected  to  prove 
or  disprove  this  statement.     At  several  mines  where  attention  is  paid 


CONDITIONS    AFFECTING    SUBSIDENCE 


to  the  cleat  no  subsidence  has  occurred,  but  there  are  a  number  of 
mines  with  rooms  opened  on  the  cleat  in  which  serious  subsidence  has 
resulted. 

Faults  and  Rolls 

GENERAL    RELATIONS    TO    SUBSIDENCE 

As  will  be  noted  later,  the  movement  of  the  overlying  beds  follow- 
ing the  mining  of  coal  may  be  influenced  greatly  by  both  the  character 
and  structure  of  the  beds  themselves.  If  faults  occur,  the  ability  of 
beds  to  arch  and  thus  to  support  the  surface  may  be  destroyed.  More- 
over, the  effects  of  subsidence  may  be  localized  if  faults  are  numerous, 
for  the  faulted  beds  over  the  mined-out  area  will  fall  in  blocks  and  will 
not  produce  long  sags  with  the  usual  draw  or  pull. 

In  almost  all  the  districts  of  the  State  faults,  slips,  and  rolls  would 
interfere  more  or  less  with  the  application  of  formulae  and  theories  of 
subsidence.  In  certain  districts,  as  will  be  noted,  these  irregularities 
are  much  more  marked.  Moreover,  the  occurrence  of  slips,  rolls, 
horses,  and  of  other  irregularities  in  the  coal  bed  itself  increases  the 
amount  of  barren  material  thrown  into  the  gob  and  thereby  the  amount 
of  filling  is  increased  and  the  amount  of  subsidence  may  be  reduced. 
When  the  rolls  or  horses  are  not  broken  by  mining  they  serve  as 
pillars  and  help  support  the  overlying  strata  if  slips  do  not  occur  along 
the  line  of  the  rolls  or  horses. 

COAL    NO.    2 

District  /.—The  geologists  report  no  important  faults,  but  nu- 
merous small  displacements  have  been  noted  in  the  coal  seam.  Both 
thrust  and  normal  faults  have  been  noted  (sec  figures  18,  19,  20,  Bull. 
10,  Illinois  Coal  Mining  Investigations).  At  many  points  the  coal 
is  thinner  and  the  roof  rolls  down. 

District  II.— "In  all  the  mines  of  this  district  numerous  small 
faults  occur,  and  horses  usually  of  a  hard  dark-gray,  micaceous  sand- 
stone are  found  in  the  vicinity  of  the  faults."14 

COAL    NO.    5 

District  /.—"A  peculiar  condition  of  the  roof  and  coal  known  lo- 
cally as  'white  top,'  exists  on  the  west  side  of  the  M.  &  Ik  mine  (see 
figure  21,  Bull.  10,  111.  Coal  Mining  Investigations)  on  the  cast  side 
of  the  Cherry  mine  (middle  bed),  and,  according  to  report,  in  the 
Cahill  mine.     At  Cherry  this  consists  of  a  white  to  gray  sandstone  or 

"Andros,  S.  O.,  Coal  mining  practice  in  District  II:  Illinois  Coal  Mining  Investi- 
gations  Bull.   7,   p.    10,   1914. 


28  SURFACE    SUBSIDENCE   IN    ILLINOIS 

sandy,  gray  shale  which  replaces  the  usual  gray  and  black  shale  of  the 
roof  and  permeates  the  coal  down  to  a  band  of  clay  found  about  14 
inches  from  the  floor.  Large  pieces  of  white  sandstone  are  found 
scattered  through  the  bed  so  that  the  whole  resembles  a  conglomerate. 
Slickenside  surfaces  are  common  throughout  the  'white  top'  areas,  and 
the  roof  is  commonly  rough  and  broken,  so  that  it  is  very  difficult  to 
keep  the  roads  clear.  The  impurities  at  some  of  these  places  exceed 
one-half  of  the  total  thickness  of  the  bed,  and  render  the  coal  worth- 
less."15 

District  IV. — Numerous  clay  veins  extend  from  the  roof  across 
the  coal  seam.16  There  are  also  many  small  faults,  slips,  and  rolls. 
Mr.  J.  A.  Udden17  has  applied  the  term  "fractures"  to  the  dislocations 
occurring  in  the  Peoria  district.  These  fractures  "are  believed  to  be 
the  result  of  physical  processes  altogether  different  from  those  causing 
faults.  In  many  places  they  have  a  close  resemblance  to  true  faults, 
but  the  direction  of  the  dislocation  is  normally  horizontal  instead  of 
normally  vertical."18 

In  the  Springfield  region  numerous  so-called  "horsebacks"  occur. 
"These  are  more  or  less  irregular  and  branching  fissures,  filled  with 
clay  or  shale,  extending  downward  from  the  overlying  beds  into  or 
through  the  coal.  They  range  in  width  from  2  or  3  inches  to  3  or  4 
feet,  the  walls  not  being  very  nearly  parallel,  and  are  considerably  and 
abruptly  wider  in  the  coal  than  in  the  overlying  roof  shale."19 

District  V. — Coal  No.  5  is  faulted  at  a  number  of  places  in  the 
district  and  contains  many  rolls.  In  several  places  an  igneous  intrusive 
penetrates  the  coal  bed  and  in  others  it  lies  in  a  sheet  at  some  distance 
above  the  coal.  Squeezes  and  subsidence  have  undoubtedly  been  in- 
fluenced greatly  by  these  irregularities  in  this  district.  Detailed  records 
of  subsidence  adjacent  to  faults  and  dikes  are  given  in  Chapter  V. 

coal  no.  6 

District  VI. — Reference  has  previously  been  made  to  the  cap  rock 
in  this  district.  In  some  places  there  are  rock  rolls  extending  down 
into  the  coal.     Minor   faults   occur,   but  they   do  not  interfere  with 


15Cady,   G.   H.,  Coal  resources  of  District  I:   111.   Coal  Mining  Investigations  Bull.   10, 
P.   78,  1915. 

10Andros,   S.   O.,   Coal  mining  practice  in  District   IV:   Illinois  Coal  Mining  Investiga- 
tions,  Bull.    12,  fig.  4,   1915. 

"Udden.  J.  A.,  Geology  and  mineral  resources  of  the  Peoria  quadrangle,  Illinois:  U.  S. 
Geol.   Survey   Bull.   506,  p.  68,   1912. 

lsAndros,   S.   O.,   Coal  mining  practice  in  District  IV :   Illinois   Coal  Mining  Investiga- 
tions Bull.    12,  fig.    5,    1915. 

19Shaw,   E.   W.  and  Savage,  T.   E..  U.   S.   Geol.   Survey   Geol.   Atlas,  Tallula-Springfield 
folio   (No.    188),  p.  3,  1913. 


CONDITIONS    AFFECTING   SUBSIDENCE  29 

mining  to  a  large  degree.  A  detailed  statement  of  faults  in  the  dis- 
trict is  given  in  the  bulletin  on  the  geology  of  the  district.20 

District  VII. — Minor  faults  or  slips  in  coal  No.  6  seam  have  been 
noted  in  Clinton,  Macoupin,  Madison,  Marion,  Montgomery,  St.  Clair, 
Perry,  Randolph,  Washington,  and  Sangamon  counties.  North  of 
Centralia  the  so-called  "Centralia  fault"  has  a  displacement  of  110 
feet.  East  of  the  Duquoin  anticline  numerous  small  faults  occur,  the 
largest  having  a  downthrow  of  20  feet.21 

District  VIII. — There  are  numerous  rolls  in  coal  No.  6  in  the 
Danville  region.  Stringers  and  lenses  of  shale  extend  down  from  the 
roof  into  the  coal.  In  places  there  are  minor  faults.  A  detailed  study 
of  the  irregularities  in  the  coal  bed  has  been  made  by  Mr.  F.  H.  Kay.22 

coal  no.  7 

District  /.—Coal  No.  7  is  quite  irregular  and  contains  horsebacks 
and  rolls  which  add  considerably  to  the  volume  of  material  thrown  into 
the  worked-out  rooms.23 

District  VIII.— Numerous  horsebacks  or  rolls  occur  in  this  bed  in 
the  Danville  district  but  they  are  not  so  extensive  as  in  coal  No.  6.24 

20Cady,  G.  H.,  Coal  resources  of  District  VI:  Illinois  Coal  Mining  Investigations 
Bull.    15,  pp.   82-87,   1916. 

21Kay,  F.  H.,  Coal  resources  of  District  VII:  Illinois  Coal  Mining  Investigation  Bull. 
11,  pp.   196  and   197,  1915. 

22Kay,  F.  H.,  Coal  resources  of  District  VIII:  Illinois  Coal  Mining  Investigations 
Bull.   14,  pp.  42-49,  1915. 

23Cady,  G.  H.,  Coal  resources  of  District  I:  Illinois  Coal  Mining  Investigations  Bull. 
10,  p.  85,  1915. 

2*Kay,  F.  H.,  Coal  resources  of  District  VIII:  Illinois  Coal  Mining  Investigations 
Bull.   14,  p.  53,  1915. 


CHAPTER  III— DAMAGE  CAUSED  BY  REMOVAL 
OF  COAL 

Contrasting  Effects  of  Longwall  and  Room-and-Pillar 

Methods 

It  may  be  said  that  in  general  the  surface  effects  of  longwall  min- 
ing are  more  uniform  than  those  resulting  from  room-and-pillar  and 
panel  working.  This  is  due  principally  to  the  gradual  sinking  of  the 
roof  in  longwall  mining  where  the  same  gradual  movement  generally 
extends  through  the  overlying  rocks  toward  the  surface.  Upon  the 
surface  the  evidences  of  subsidence  will  be  a  gentle  sag,  and  where 
the  longwall  face  is  stopped  there  may  be  a  more  or  less  well-defined 
terrace  outlining  in  a  general  way  the  area  that  has  been  undermined. 
Except  in  a  shallow  working  and  in  faulted  areas  probably  no  large 
surface  cracks  or  breaks  will  occur,  and  if  these  do  occur  they  will 
usually  close  after  the  longwall  face  has  advanced  some  distance 
beyond  the  point  in  the  mine  vertically  below. 

On  the  other  hand,  where  coal  has  been  mined  by  other  systems, 
the  area  over  which  the  settling  may  extend  is  generally  smaller,  and 
serious  cracks  and  breaks  are  more  likely  to  result. 

Surface  Evidences  of  Subsidence 

In  general,  it  may  be  said  that  the  principal  ways  in  which  sur- 
face movement  is  shown  are  by :  (1)  surface  cracks  and  displace- 
ments, (2)  pit  holes  or  caves,  and  (3)  sags.  The  sags  and  holes  fre- 
quently hold  accumulations  of  surface  water. 

surface  cracks  and  displacements 

As  previously  noted,  serious  cracks  have  not  been  observed  fre- 
quently in  the  longwall  district  of  Illinois.  One  of  the  reasons  that 
no  surface  cracks  are  evident  is  the  presence  of  a  heavy  blanket  of 
glacial  drift  from  25  to  200  feet  thick  lying  over  the  "Coal  Measures" 
in  this  district.  At  various  points  where  the  workings  have  been  shal- 
low, the  rock  cover  thin,  and  the  surficial  beds  saturated  with  water, 
serious  breaks  have  resulted  accompanied  by  a  rush  of  sand,  mud,  and 
water  into  the  mine.  The  resulting  break  upon  the  surface  is  however 
not  typical  of  longwall  mining,  ?nd  this  type  of  break  is  as  likely  to 
occur  in  room-and-pillar  mining.  In  Europe  at  various  points  in  the 
longwall  coal  mining  districts,  cracks  several  inches  wide  have  been 
observed  above  longwall  workings  over  1,000  feet  deep. 

(30) 


DAMAGE   BY    COAL   REMOVAL 


31 


The  surface  cracks  that  have  been  observed  have  been  due  to  ten- 
sion and  to  shear.  Where  the  coal  has  been  removed  over  a  large 
area  in  room-and-pillar  mining,  the  roof  if  unsupported  sinks  gradually, 
and  if  it  does  not  break  will  in  time  rest  upon  the  floor.  In  longwall 
mining,  the  roof  settles  upon  the  gob  and  compresses  it  so  that  in  time 
it  occupies  a  volume  equal  to  only  a  small  fraction  of  the  volume  of 


Fig.   5. — Diagrammatic  illustration   showing  angle   of  break  and   angle  of 
subsidence    (after  Wachsmann). 


the  excavation,  depending  upon  the  nature  and  the  amount  of  the  fill- 
ing. As  the  immediate  roof  sinks  the  overlying  beds  also  sink,  and 
stresses  are  set  up  in  the  various  beds  successively  from  the  immediate 
roof  to  the  surface  rocks  (fig.  5).  If  each  stratum  is  regarded  as  a 
beam,  a  portion  of  the  beam  will  be  in  tension  and  a  portion  in  com- 
pression.    As  the  ordinary  rock  of  mine  roofs  is  much  weaker  in  ten- 


32 


SURFACE   SUBSIDENCE  IN   ILLINOIS 


sion  than  in  compression,  cracks  due  to  tension  will  appear  before 
the  evidences  of  compression.  Tension  cracks  may  be  found  in  the 
mine  roof  in  the  zone  where  tension  is  greater  than  the  tensile  strength 
of  the  rocks,  and  similarly,  upon  the  surface  tension  cracks  may  be 
found  in  the  rocks  or  in  consolidated  surficial  beds  in  the  tension  zone. 
Where  there  has  been  an  extensive  sag  over  a  worked-out  area,  tension 
cracks  are  likely  to  occur  around  the  perimeter  of  the  sag.  Figure  6 
shows  a  tension  crack  from  4  to  10  inches  wide  occurring  over  a  room- 
and-pillar  mine  in  the  Streator  district. 


Fig.  6. — Crack  in  the  soil,  caused  by  room-and-pillar  mining  at  a  shallow 
depth  at  Streator. 


In  a  mine  on  coal  No.  6  in  Franklin  County  a  number  of  squeezes 
have  resulted  in  surface  subsidence.  The  shaft  is  550  feet  deep  and 
the  coal  9  to  10  feet  thick,  from  1  to  2  feet  being  left  as  roof  coal.  The 
mine  is  worked  in  panels,  room  centers  being  40  feet  and  pillars  18  feet 
(fig.  7).  No  pillars  have  been  drawn.  In  two  panels  there  has  been 
movement  which  has  affected  the  surface.    At  "A"  the  crack  is  8  to  10 


DAMAGE   BY   COAL    REMOVAL 


33 


inches  wide  and  at  "B"  there  are  two  cracks,  one  of  which  is  2  to  3 
inches  wide  (figs.  8  and  9). 

Where  the  mine  roof  fails  by  shear  along  the  pillars  or  supports, 
the  entire  overlying  mass  may  be  dropped  into  the  excavation,  and  a 
more  or  less  sharp  break  may  appear  on  the  surface.  Where  the  fallen 
mass  is  large,  a  series  of  breaks  may  occur,  as  shown  in  figure  10. 
In  the  opinion  of  a  number  of  prominent  American  engineers  the 
strata  above  the  immediate  roof  frequently  fail  by  shear. 

As  previously  noted  the  mine  roof  is  likely  to  fail  first  in  tension, 
and  readjustment  is  likely  to  precede  failure  under  compression.     If 


SIS 


fii 


TTrnn 


PPfPfi'* 


DOCK 


r 


Fig.  7.— Plan  of  two  panels  of  a  Franklin  County  mine,  550  feet  deep. 
Subsidence  caused  surface  cracks  as  indicated.  Over  the  north  panel  at  A  the 
crack  was  8  to  10  inches  wide,  and  at  B  were  two  smaller  cracks. 

great  lateral  pressure  and  a  free  or  unconfined  surface  exist,  buckling 
may  result,  as  illustrated  in  the  heaving  of  the  rock  floor  in  deep  mines 
and  tunnels.  One  of  the  best  illustrations  of  this  type  of  movement 
occurred  in  the  Simplon  tunnel  in  Europe.1 

Where  there  is  a  sag  over  an  extensive  area  or  subsidence  over 
an  excavation  of  considerable  height,  the  surface  of  the  central  position 
of  the  basin  may  be  subjected  to  severe  stresses  in  compression.  This 
will  result  in  the  elevation  of  this  central  area  relative  to  the  adjacent 
portion  of  the  subsiding  ground,  although  the  entire  mass  may  be  sink- 
ing.   If  the  uppermost  stratum  is  rock  or  hard  material,  such  as  frozen 


'Lauchli,   E.,  Tunneling,  fig.   92,  p.  95,   1915. 


34 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


soil,  this  compression  may  result  in  buckling,  and  small  anticlines  may 
result,  as  shown  in  figure  11. 

PIT    HOLES   OR   CAVES 

Where  shallow  mining  is  carried  on,  falls  of  mine  roof  are  fre- 
quently  followed  by   surface  subsidence  causing  pit   holes  or   caves. 


Fig  8.— Crack,  8  to  10  inches  wide,  due  to  subsidence  over  the  north  panel 
shown  in  figure  7.  The  view  was  taken  from  A  looking  west.  (Photo  by  J.  R. 
Fleming,  U.   S.   Bureau  of  Mines.) 

If  the  rock  cover  is  not  thick  and  the  surficial  beds  are  heavy  and  loose, 
the  mine  openings  may  be  filled  by  a  rush  of  surficial  material,  so  that 
the  pit  hole  may  have  a  much  greater  volume  than  the  single  mine 
chamber  in  which  the  break  occurred.  Such  pit  holes  may  appear  di- 
rectly over  many  worked-out  rooms  and  may  destroy  entirely  the  value 
of  the  surface  for  agriculture  and  for  building  sites.    When  subsidence 


DAMAGE   BY   COAL   REMOVAL 


35 


has  ceased,  the  surface  may  be  restored  by  filling.    Pit  holes  of  various 
types  are  illustrated  in  figures  12  to  18. 

When  the  surface  beds  are  cemented  material,  frequently  called 
"hard  pan,"  an  arch  may  tend  to  form  across  from  one  pillar  or  wall 
to  another.     Falls  may  extend  close  to  the  surface  and  be  concealed 


Fig.  9.— Cracks  over  south  side  of  panel  shown  in  figure  7.     The  view  was 
taken  from  B  looking  east.     (Photo  by  J.  R.  Fleming,  U.  S.  Bureau  of  Mines.) 


by  a  thin  covering  of  a  resistant  bed.  Eventually  this  last  bed  may 
break,  and  the  fall  may  show  the  large  cave  beneath,  as  illustrated  by 
figure  19.  Where  the  soil  is  covered  by  a  heavy  sod,  the  dangerous 
:ondition  of  the  fields  may  be  concealed  for  a  time  owing  to  the  tenacity 
3f  the  sod.  Heavy  sheets  of  sod  may  be  seen  (fig.  20)  hanging  over 
the  rim  of  breaks,  and  instances  have  been  reported  in  which  for  a 
:onsiderable  time  simply  a  sod  roof  has  concealed  caves  several  feet 
in  diameter. 


36 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


FlG  10— Cracks  and  breaks  due  to  shear.  View  along  the  rim  of  a  large 
pit  hole  caused  by  an  extensive  movement  into  a  shallow  mine.  In  the  right  fore- 
ground the  mass  of  earth  has  dropped  18  inches. 


Fig  11— Buckling  of  frozen  sod  due  to  compression  along  the  axis  of  a 
basin  or  sag.  The  movement  occurred  over  a  large  excavation  in  a  shallow  mine. 
The  sod  in  the  foreground  was  lifted  as  much  as  two  feet. 


DAMAGE   BY   COAL   REMOVAL 


37 


^%  M 


Fig.  12.— Surface  breaks  in  a  field  near  Carterville.  The  shaft  is  120  feet 
deep,  and  a  7-foot  bed  of  coal  is  being  mined.  The  roof  is  slate  and  the  over- 
burden clay;  no  quicksand  has  been  noted.  The  breaks  are  about  20  feet  in 
diameter  and  from  a  few  feet  to  as  much  as  20  feet  deep. 


Fig.  13.— Surface  breaks  extending  over  a  room  in  a  mine  near  Harrisburg 
where  the  coal  is  7  feet  thick  and  80  feet  deep.  The  rooms  are  24  feet  wide  and 
have  24-foot  pillars. 


58 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


Fig.   14.— Plan   showing  workings  of  a  mine  and  location  of   subsidence 
movements  adjacent  to  a  dike. 


Fig.  15.— Plan  of  a  mine  showing  a  few  details  of  movement  near  a  dike. 


DAMAGE    BY    COAL    REMOVAL 


39 


Fig.   16. — Breaks  in  a  pasture  over  an  abandoned  mine  west  of   Danville 
where  the  coal  is  6  feet  thick  and  100  feet  deep. 


Fig.  17. — Side-hill  breaks  near  Cuba  caused  by  room-and-pillar  mining  of 
a  5-foot  bed  of  coal  from  50  to  75  feet  deep. 


40 


SURFACE    SUBSIDENCE    IN    ILLINOIS 


Fig.  18.— Large  area  covered  by  pit  holes  in  the  suburbs  of  a  town  in  cen- 
tral Illinois  where  a  5-foot  bed  of  coal  is  being  mined  at  a  depth  of  75  to  100 
feet.     Trees  are  falling  into  the  pit  holes ;  the  houses  are  being  used. 


pIG  19.— Cave-in  on  land  south  of  Dewmaine  where  a  9-foot  bed  of  coal 
is  being  mined  at  a  depth  of  100  feet.  The  opening  is  12  feet  in  diameter  and  15 
feet  below  the  surface ;  the  width  is  approximately  25  feet.  The  hard  pan  arches 
up  from  the  shale. 


DAMAGE    BY    COAL    REMOVAL 


41 


Where  the  breaks  occur  on  hillsides,  a  series  of  resulting  move- 
ments may  be  clue  to  the  natural  slope  of  the  ground.  The  more  or 
less  concentric  rings  formed  by  these  breaks  are  shown  in  figure  21. 


Fig.  20. — Detail  of  a  cave  on  a  hillside  near  Streator;  note  the  hanging  sod. 

A  serious  condition  is  illustrated  in  figure  22  where  the  surface 
is  owned  by  one  mining  company  as  a  site  for  company  houses,  and  the 
coal  is  owned  and  mined  by  another  company.  The  owner  of  the  coal 
is  reported  to  be  mining  from  8  to  1 1   feet  of  coal  at  a  depth  of  100 


-Side 


1  lAl  L  i 


i 


m 


1  *^ifc&** 


illow   workings  near   Streator. 


feet  by  the  room-and-pillar  method.  The  owner  of  the  surface  se- 
cured an  injunction  restraining  the  mining  of  coal  under  the  buildings 
shown  in  the  illustration.  The  court  would  not  restrain  mining  under 


42 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


the  other  portions  of  the  tract  as  any  damage  resulting  might  be  the 
basis  for  a  suit. 


SAGS 


Where  the  workings  are  covered  by  thicker  and  stronger  beds  of 
rock,  and  the  area  excavated  is  larger,  the  surface  effects  of  subsidence 
may  be  sags  instead  of  breaks,  caves,  or  pit  holes.    During  part  of  the 


C5CT-0—  = 


O 

o 


\r 


Hl  o° 


Scale 
100  200  300  feet 


L 

r 


Fig.  22.— Plan  of  a  40-acre  tract  in  southern  Illinois,  showing  relation  of 
approximately  60  pit  holes  to  the  underground  workings. 

year  these  sags  may  contain  pools  of  water,  and  if  they  are  considerably 
below  the  previous  drainage  levels,  they  may  be  inundated  continually. 
In  the  longwall  field  of  northern  Illinois  it  is  necessary  to  provide 
artificial  drainage  for  much  of  the  land  which  is  otherwise  suited  for 
agricultural  purposes.     Figure  23  shows  the  nature  of  the  topography 


DAMAGE   BY    COAL    REMOVAL 


43 


in  the  Coal  City-Wilmington  area.  It  is  evident  that  subsidence  re- 
sulting from  mining  operations  may  seriously  derange  the  artificial 
drainage  systems  which  are  installed.  Figure  24  shows  a  pond  formed 
over  a  sag  due  to  longwall  mining  near  Coal  City. 


Fig.  23. — Topographic  map  of  the  Coal  City- Wilmington  area. 


In  a  portion  of  a  mine  in  Perry  County  (fig.  25)  opened  on  coal 
No.  6  at  a  depth  of  350  feet  the  coal  averages  9  to  11  feet,  but  the 
upper  bench  of  3  feet  is  not  mined.  Six  sags  but  no  surface  breaks 
have  resulted  from  the  mining.  In  general  the  pillars  have  not  been 
drawn.  In  one  place  where  pillars  have  been  drawn  an  area  600  feet 
in  diameter  sagged,  the  maximum  depression  being  4  feet;  the  subsi- 


44  SURFACE    SUBSIDENCE   IN    ILLINOIS 

dence  of  the  surface  began  twenty-four  hours  after  the  movement  was 
observed  underground.  Another  area  800  feet  in  diameter  with  a 
maximum  depression  of  3  feet  was  noted  at  the  same  mine. 

At  a  mine  in  Franklin  County  where  the  coal  seam  is  9  feet 
thick,  one  foot  of  the  top  coal  is  left  in  mining.  The  shaft  is  approxi- 
mately 450  feet  deep.  The  roof  is  gray  shale,  and  no  limestone  occurs 
immediately  over  the  coal.  The  bottom  is  fire  clay  varying  from  a 
few  inches  to  5  feet.  A  number  of  squeezes  have  occurred,  principally 
where  the  rooms  have  been  turned  on  45-foot  centers  with  15-foot 
pillars.  The  rooms  were  carried  250  feet  and  it  was  planned  to  leave 
a  20-foot  barrier  between  panels  of  rooms.  In  places  the  room  necks 
have  been  turned  wide,  and  the  room  cross-cuts  have  been  driven  about 
20  feet  wide.  The  main  entries  are  protected  by  a  barrier  pillar  of 
110  feet,  the  cross-entries  have  been  driven  on  25-  and  on  50-foot 
centers. 


Fig.  24. — Pond  in  a  sag  due  to  longwall  mining  at  Coal  City,  where  a  3-foot 
bed  is  being  removed  at  a  depth  of  135  feet. 


Several  squeezes  had  taken  place  where  pillars  had  been  drawn, 
particularly  on  one  panel  in  the  northeastern  section  of  the  mine.  In 
November,  1914,  an  extensive  movement  began  underground  in  the 
panel  adjoining  on  the  east  a  panel  that  had  previously  squeezed,  and 
surface  subsidence  resulted.  Mining  had  been  completed  in  this 
panel  2  to  3  months  previous.  The  movement  continued  several  weeks, 
and  a  large  fall  occurred  on  the  night  of  December  9,  1914.  Falls 
continued  for  4  hours,  and  the  following  morning  there  were  evi- 
dences of  surface  movement.  A  railroad  bridge  had  subsided  18 
inches,  concrete  sidewalks  cracked  in  some  places  (see  figure  48)  or 
broken  by  buckling  in  others,  telephone  poles  were  tipped  (see  figure 
26),  and  foundations  of  houses  were  cracked.     Later  when  the  snow 


DAMAGE    BY    COAL    REMOVAL 


45 


thawed,  the  lateral  extent  of  the  movement  was  evidenced  by  the 
ponds  which  covered  a  large  area  (see  figure  46).  From  the  data  at 
hand  no  evidence  showed  that  at  the  end  of  two  weeks  the  depressions 
were  more  than  18  inches  deep.  However,  at  the  end  of  three  months 
the  subsidence  at  places  was  as  much  as  4  feet. 


1711 
IU! 


-<r vt- ii—  -w — ii 


i  lvjc  jcri  cdc  dc5c5  cj&cjczjc  5c5  c  : 

T- -if — inr 


NUv_ 

j'JL_- 

PC  Subsidence 

J 

-'jn!v- 

j| 

---3,-".': 

J^-- 

£r-     No.  |5f= 

_  ;T 

5  !-•'--. 

-L,_ a,---  ,V 

\-J 

:3!jc: 

^ 

--''p.''. 

nil  ni- 1  cn'J  •-  l.U>  •: 


Fig.  25.— Plan  of  a  mine  in  Perry  County  showing  relation  of  sags  to  under- 
ground workings. 


The  subsidence  occurred  over  an  area  of  44  rooms  in  a  panel  in 
which  the  entry  pillars  were  20  feet  wide.  The  cut-throughs  in  the 
rooms  were  staggered  60  feet  apart  and  were  20  feet  wide.    Where  the 


46 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


room  barrier  on  the  west  had  been  broken  through,  the  squeeze  worked 
over  into  the  zone  which  had  previously  subsided.  Where  the  barrier 
pillar  was  still  intact,  it  was  sufficient  to  check  the  movement,  and 
directly  above  on  the  surface  tension  cracks  appeared  extending  in  the 
same  general  direction  as  the  barrier  pillar.  There  was  a  gentle  sag 
to  the  east  between  the  room  barrier  and  the  entry  pillar.  As  this 
pillar  was  small  and  broken  by  cross-cuts,  the  squeeze  rode  over  it, 


Fig.  26. — Telephone  poles  tipped  toward  a  sag  over  a  Franklin  County  mine 
where  an  8-foot  coal  is  being  removed  at  a  depth  of  450  feet. 


and  some  subsidence  resulted,  although  the  deepest  portion  of  the 
sag  was  transversely  across  the  panel  of  rooms.  The  underground 
movement  covered  an  area  approximately  500  by  1,000  feet. 

In  April,  1915,  at  the  same  mine,  squeezes  occurred  in  two  ad- 
joining panels  each  of  which  consisted  of  32  rooms.    The  rooms  were 


DAMAGE    BY    COAL   REMOVAL 


47 


turned  with  wide  necks  and  were  worked  out  quickly.  No  pillars 
were  drawn.  About  3  months  after  the  rooms  had  been  finished,  a 
severe  squeeze  began.  The  easterly  panel  was  badly  crushed  in  3  days, 
and  the  squeeze  rode  over  the  small  barrier  to  the  next  panel  on  the 
west.  Falls  began  in  the  west  panel  on  the  fifth  day  and  continued 
for  about  one  week.  At  the  end  of  two  weeks  no  evidence  showed 
that  any  considerable  surface  movement  had  occurred.  In  July,  1915, 
the  next  panel  east  caved,  and  in  a  few  days  several  sidewalks  were 
cracked  and  tension  cracks  appeared  in  the  dry  earth. 

In  many  districts  room-and-pillar  mining  has  caused  extensive 
sags  which  have  eventually  become  swamps.  The  trees,  unsuited  to 
the  changed  conditions,  have  been  killed  and  the  entire  area  has  become 


•>  ia'TjE:.  ?-.*'•"  ukJ 


Fig.  27. — Swamp  in  a  typical  sag  in  Randolph  County  where  a  6- foot  coal 
is  being  mined  at  a  depth  of  150  feet.  The  rooms  are  on  50- foot  centers;  pillars 
18    feet. 


a  waste.  Somewhat  typical  illustrations  of  such  swamps  are  shown  in 
figures  27  to  31. 

Frequently  swamps  of  this  nature  are  formed  in  the  spring  within 
fields  and  interfere  with  the  plowing  and  planting.  During  the  sum- 
mer these  ponds  may  dry  up,  and  as  a  result  there  may  be  within  fields 
large  untilled  and  wasted  areas. 

In  figure  31  is  shown  a  Vermilion  County  cornfield  containing  an 
unworked  area  at  least  200  feet  square.  Similar  conditions  have  been 
noted  in  many  of  the  coal   districts    (fig.  32).     Not  only  may  occa- 


48 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


sional  ponds  be  created,  but  at  times  large  sections  may  be  lowered 
beneath  the  flood  levels  of  river  bottoms.  There  has  been  considerable 
litigation  in  northern  Illinois  where  coal  is  being  mined  in  the  Illinois 
River  bottom.     It  has   been  claimed   by  property  holders   that  lands 


Fig.  28. — Pond  4  feet  deep  and  covering  an  area  of  about  an  acre,  due  to 
subsidence  near  Clifford,  where  a  coal  bed  about  7  feet,  6  inches  is  being  mined 
at  a  depth  of  140  feet.  Considerable  quicksand  occurs  in  the  vicinity.  The 
rooms  are  driven  20  to  22  feet  wide  on  40-foot  centers,  and  no  pillars  are  drawn. 


Fig.  29. — Flooding  of  a  large  tract  in  Franklin  County  caused  by  mining 
of  a  8-foot  coal  at  a  460-foot  depth.  Rooms  were  carried  30  feet  wide  on  45-foot 
centers ;  no  pillars  were  drawn. 


were  inundated  on  account  of  the  increased  amount  of  water  flowing 
into  Illinois  River  due  to  the  discharge  through  the  Chicago  Drainage 
Canal.     On  the  other  hand  the  officers  of  the  Chicago  Sanitary  Dis- 


DAMAGE    BY    COAL    REMOVAL 


49 


Fig.  30.— Pond  caused  by  subsidence  at  Westville,  Vermilion  County,  where 
6  feet  of  coal  was  removed  by  room-and-pillar  mining  at  a  depth  of  210  feet. 
Levels  at  surface  show  maximum  depth  of  sag  to  be  4.7  feet.  (Photo  by  R.  Y. 
Williams.) 


y. 


■«■**>- 


v 


Fig.  31.— Open  space  south  of  Danville  about  200  feet  square  in  cornfield, 
indicating  the  area  is  not  tilled  because  water  stands  over  the  sag  in  the  spring. 


Fig.  32. — Drowned-out  area  of  corn  near  Nokomis  where  the  8-foot  coal 
bed  is  worked  at  a  depth  of  about  625  feet. 


50  SURFACE   SUBSIDENCE   IN    ILLINOIS 

trict  claimed  that  the  lands  were  flooded  because  coal-mining  operations 
lowered  the  lands  beneath  the  former  drainage  levels. 

Agriculture  and  Surface  Subsidence 
importance  of  agriculture 
Illinois  is  preeminently  an  agricultural  and  manufacturing  state. 
To  the  manufacturing  interests  an  ample  and  continuing  fuel  supply 
is  of  prime  importance.  In  few  states  are  both  agriculture  and  manu- 
facturing developed  to  so  great  an  extent,  and  in  practically  no  other 
state  do  the  coal  beds  underlie  so  extensive  and  so  fertile  farm  lands. 
In  a  large  part  of  the  Appalachian  and  the  western  coal  fields  the  sur- 
face is  almost  valueless  for  agricultural  purposes,  but  where  the  over- 
lying surface  is  tilled  it  is  of  much  less  value  than  the  farm  lands  of 
Illinois. 

EXTENT   AND   VALUE   OF   FARM    LANDS 

In  the  accompanying  tables  are  given  data  from  the  United  States 
States  Census  for  1910  showing  the  percentage  of  the  area  in  farm 
lands,  the  average  value  of  the  land  per  acre,  and  also  the  value  of 
the  coal  produced  in  1910. 

The  farm  lands  of  Pennsylvania  constituted  64.8  per  cent  of  the 
area  of  the  State,  whereas  only  68.2  per  cent  of  the  farm  land  was 
improved,  or  44.2  per  cent  of  the  total  area  of  the  State.  In  the  lead- 
ing bituminous  county  of  Pennsylvania  (Table  4)  62.6  per  cent  of 
the  land  was  in  farms,  and  in  Washington  County,  which,  among  the 
coal  counties  ranks  high  in  the  fertility  of  soil,  the  percentage  of  total 
area  in  farms  was  91.3.  In  the  three  counties  important  as  anthracite 
producers,  the  percentage  of  area  in  farms  ranges  from  43.5  to  47.2. 
The  average  value  of  land  per  acre  in  Pennsylvania  was  $33.92 ;  in  the 
five  leading  bituminous  counties  (excluding  Allegheny2)  the  range  was 
from  $22.01  to  $55.21 ;  whereas  in  the  anthracite  counties  the  range 
was  from  $25.03  to  $33.68. 

In  the  leading  coal-producing  county  in  West  Virginia  only  37.8 
per  cent  of  the  land  was  in  farms,  and  13.6  per  cent  of  the  farm  land 
was  improved  or  5.14  per  cent  of  the  area  of  the  county.  The  average 
value  of  the  land  per  acre  was  $33.42.  In  one  important  coal-producing 
county  93.1  per  cent  of  the  land  was  in  farms,  yet  the  average  value  was 
only  $43.81  per  acre. 

In  Kentucky  86.3  per  cent  of  the  land  was  in  farms,  and  64.7 
per  cent  of  the  farm  land  was  improved  or  55.84  per  cent  of  the  total 

2The  census  reports  the  average  value  of  land  per  acre  in  Allegheny  County  to  have 
been  $146.21.  This  high  value  is  due  to  the  fact  that  Pittsburgh  and  Allegheny  are  located 
in  this  county. 


Fig.  33. — Map  showing  relation  of  different  thicknesses  of  coal  to  the  values 
of  farm  lands  as  given  in  the  1910  census. 


52  SURFACE    SUBSIDENCE   IN    ILLINOIS 


area. 


The  average  value  of  the  land  was  $21.83  per  acre.  In  one  of 
the  leading  coal-producing  counties  of  Kentucky  81.2  per  cent  of  the 
area  is  in  farms,  and  29.2  per  cent  improved,  or  23.71  per  cent  of  the 
total  area.    The  land  in  this  county  has  an  average  value  of  $11.72. 

In  Illinois  90.7  per  cent  of  the  area  was  in  farms,  and  86.2  per 
cent  of  the  farm-land  area  was  improved,  or  the  improved  land  was 
78.18  per  cent  of  the  area  of  the  State.  The  average  value  of  the  land 
per  acre  was  $95.02.  In  Sangamon  County,  an  important  coal  pro- 
ducer, 87.33  per  cent  of  the  land  was  improved,  which  is  9  per  cent 
better  than  the  average  for  the  State.  The  average  price  of  land  in 
Sangamon  County  was  $138.30  per  acre,  a  value  of  $43  more  than  the 
average  for  the  State.  The  average  price  in  Vermilion  County,  another 
important  coal  producer,  was  $138.85.  The  average  price  for  La  Salle 
County  was  $142.92.  In  the  southern  coal  counties  the  farm  lands  are 
less  valuable,  but  in  Franklin  and  Williamson  counties  the  percentage 
of  land  improved  is  greater  than  in  the  best  counties  of  any  of  the 
states  previously  mentioned,  whereas  the  average  prices  per  acre,  $38.43 
and  $30.61  respectively,  compare  favorably  with  the  average  prices 
of  lands  in  the  other  states. 

With  the  "Coal  Measures"  covering  66.9  per  cent  of  the  entire 
area  of  Illinois,  and  over  90  per  cent  of  the  area  of  the  State  in  farms, 
the  average  value  of  which  is  at  present  greater  than  the  average  price 
of  coal  rights,  the  problem  in  Illinois  of  protecting  the  surface,  par- 
ticularly agricultural  lands,  is  much  different  and  much  more  important 
than  the  problem  in  most  of  the  other  coal-mining  states.  As  pre- 
viously noted,  over  15,000  square  miles  are  underlain  by  coal  beds  over 
4  feet  thick,  and  at  least  10,000  square  miles  additional  carry  a  bed  3 
feet  thick.  Beds  no  thicker  than  3  feet  are  being  mined  in  Illinois  and 
in  other  states ;  and  it  is  only  a  matter  of  time  until  the  problem  of 
lowering  the  surface  of  one-half  the  State  by  an  appreciable  amount 
must  be  considered,  if  at  least  a  fair  extraction  of  the  coal  is  desired. 
The  average  value  of  land  per  acre  in  the  counties  in  the  coal  districts 
of  Illinois  is  shown  in  Table  4  and  on  figure  33. 


DAMAGE    BY    COAL   REMOVAL 


53 


Table  4. — Value  of  farm  lands,  April  15,  igio,  (U.  S.  Census) 


States  and  counties 


Approx. 
land    area 


Illinois 35 

Bureau    

Christian    

Clinton   

Franklin     

Fulton     

Gallatin    

Greene    

Grundy  

Henry   

Jackson     

Jefferson    

Knox     

La  Salle  

Livingston     

Logan   

Macon     

Macoupin 

McDonough    . .  . 

McLean    

Madison     

Marion    

Marshall     

Menard 

Mercer    

Montgomery    ... 

Moultrie  

Peoria  

Perry     

Randolph   

Rock  Island    .... 

St.  Clair  

Saline    , 

Sangamon    , 

Shelby    

Stark  

Tazewell     

Vermilion     , 

Warren     

Washington     .... 

White    

Will  

Williamson  

Woodford  


Acres 

,867,520 

563,840 

448,000 

309,120 

284,800 

565,760 

216,320 

329,600 

277,120 

527,360 

376,320 

385,920 

455,040 

733,440 

667,520 

394,880 

374,400 

550,400 

376,320 

762,240 

471,680 

364,160 

253,440 

202,880 

345,600 

440,960 

216,320 

407,040 

288,640 

375,680 

271,360 

424,320 

255,360 

560,640 

494,080 

185,600 

414,080 

589,440 

349,440 

359,040 

324,480 

540,160 

287,360 

337,920 


Land 
in  farms 


Acres 
32,522,937 
524,455 
422,520 
280,440 
222,578 
506,222 
162,693 
308,579 
249,984 
504,927 
305,759 
336,340 
424,381 
662,755 
646,551 
381,478 
356,946 
511,225 
353,776 
733,161 
408,487 
335,624 
232,456 
192,910 
326,311 
426,398 
207,249 
353,206 
234,915 
323,237 
237,936 
364,523 
213,831 
520,999 
461,878 
175,719 
374,528 
534,385 
326,653 
329,135 
285,027 
498,651 
227,642 
316,064 


n^O-S 


Value  of 

coal* 

production 

in  1910 


90.7 

93.0 

94.3 

90.7 

78.1 

89.5 

75.2 

93.6 

90.2 

95.7 

81.2 

87.2 

93.3 

90.4  ! 

96.9 

96.6 

95.3 

92.9 

94.0 

96.2 

86.6 

92.2 

91.7 

95.1 

94.4 

96.7 

95.8 

86.8 

81.4 

86.0 

87.7 

85.9 

83.7 

92.9 

93.5 

94.7 

90.4 

90.7 

93.5 

91.7 

87.8 

92.3 

79.2 

93.5 


86.2 
87.9 
96.4 
87.2 
86.8 
70.6 
86.0 
79.3 
91.6 
90.6 
71.7 
85.2 
81.6 
91.3 
97.5 
95.7 
95.9 
80.2 
85.7 
96.0 
86.8 
85.5 
84.2 
91.7 
83.2 
89.4 
94.2 
80.3 
80.2 
76.8 
77.7 
84.9 
85.9 
94.0 
92.1 
91.4 
87.7 
93.6 
86.5 
82.6 
92.1 
89.2 
84.4 
87.4 


$95.02 

114.53 

123.63 

44.59 

38.48 

88.18 

48.60 

72.52 

124.50 

112.03 

31.27 

34.62 

112.69 

142.92 

161.76 

156.49 

161.29 

69.74 

116.89 

171.85 

70.53 

39.45 

123.92 

122.04 

104.63 

73.49 

154.95 

107.67 

30.62 

36.11 

87.97 

81.57 

39.88 

138.30 

88.22 

123.10 

144.21 

138.85 

129.80 

34.02 

55.44 

104.08 

30.61 

154.27 


52,405,897 

1,488,070 

1,322,162 

1,092,752 

2,312,342 

2  253,307 

85,000 

14,330 

968,563 

225,018 

776,363 

15,000 

54,174 

2,032,002 

262,056 

469,657 

387,713 

3,479,049 

61,194 

29,470 

4,222,078 

801,117 

466724 

464,375 

343,115 

1,907,006 

3  800 

1,042,478 

1.411,553 

1,065,969 

109,433 

5,763,249 

2,713,514 

5,014,237 

179,291 

53,056 

210,824 

2,691,574 

5,086,928 

22,500 

27,172 

126,362 

5,086,928 

121,131 


Mineral   Resources  of  United  States  for   1910,   U.   S.   Geol.    Survey,   1911. 


54  SURFACE    SUBSIDENCE   IN    ILLINOIS 

Table  4.— Value  of  farm  lands,  April  15,  igio,  (U.  S.  Census)— Concluded 


1 
States  and  counties 

Approx. 
land   area 

Land 
in  farms 

en 

v  rt  c3 

£"3-9 

Per  cent  of 
farm  land 
improved 

Average 
value  of 
land  per 
acre 

Value  of 

coal* 

production 

in  1910 

Kentucky    

Henderson     

Hopkins    

A  cres 
25,715,840 
278,400 
349,440 
302,080 
373,760 
498,560 
28,692,480 

464,000 
458,886 
730,880 
508,800 
551,680 
664,960 

288,640 
570,880 
497,280 

25,767,680 
339,840 
268,800 

15,374,080 
426,880 
266,240 
550,400 
341,120 
201,600 
382,080 

Acres 
22,189,127 
231,677 
298,263 
245,210 
338,211 
481,370 
18,586,832 

308,342 
228,004 
271,094 
318,475 
503,923 
493,491 

134,160 
269,486 
216,348 
19,495,636 
270,581 
122,874 
;  10026,442 
110,142 
247,835 
252,402 
128,784 
173,529 
139,134 

86.3 
83.2 
85.4 
81.2 
90.5 
96.6 
64.8 

66.5 
49.7 
37.1 
62.6 
91.3 
74.2 

46.5 
47.2 
43.5 
75.7 
79.6 
45.7 
65.2 
25.8 
93.1 
45.9 
37.8 
86.1 
36.4 

64.7 
86.7 
60.7 
29.2 
55.1 
26.3 
68.2 

79.4 

57.2 
59.5 
66.4 
85.7 
74.9 

43.8 
51.1 
65.8 
50.6 
60.7 
41.8 
55.1 
48.8 
84.6 
53.8 
13.6 
76.0 
46.9 

21.83 
36.08 
20.28 
11.72 
9.97 
8.82 
33.92 

146.21 
32.59 
22.01 
55.21 
48.03 
42.03 

33.68 
28.64 
25.03 
20.24 
34.58 
22.79 
20.65 
24.72 
43.81 
23.45 
33.42 
39.91 
27.15 

14,405,887 

239,332 

2  202,299 

Muhlenberg  

Ohio    

Pike  

Pennsylvania    

Bituminous — 

Allegheny    ........ 

2,503,371 

746,611 

869,501 

313,304,812 

20,359,650 
17,566,903 

Clearfield    

Fayette    

Washington     

Westmoreland    . . . 
Anthracite — 

Lackawanna    

8,048,056 
31,210,480 
17,567,634 
22,389,051 

36,868,765 
52,759,185 

Schuylkill     

Virginia     

Tazewell     

Wise    

28,998,199 
5,877,486 
1,169,981 
3,274,809 

West  Virginia    

Fayette    

Harrison    

Kanawha    

McDowell    

56,665,061 

10,135,369 

3,814,791 

6,518055 

12,767,998 

4,165,737 

Raleigh   

3,309,67c1 

^Mineral  Resources 

of  United  St 

ites  for    1910, 

u.  s.  c 

i'eol.   Sur 

vey,   191 

1. 

VALUE    OF    COAL    LANDS 

Although  it  is  impossible  to  give  an  average  value  for  coal  lands 
in  Illinois,  yet  it  may  not  be  out  of  place  to  indicate  at  what  prices  coal 
lands  and  coal  rights  are  being  sold.  From  these  data  some  idea  of 
the  relation  between  the  present  value  of  the  surface  and  of  the  coal 
can  be  obtained,  and  possibly  a  better  idea  of  the  prospective  value  of 
Illinois  coal  may  be  secured  by  a  study  of  these  data. 

In  a  report3  on  the  value  of  coal  land  made  by  the  United  States 
Geological  Survey  in  1910,  the  following  royalty  rates  per  ton  of  mine- 


:!Ashley,   G.   H.,   Valuation   of  public   coal  lands:   U.   S.   Geol.   Survey  Bull.  424,  p. 


1910. 


DAMAGE    BY    COAL    REMOVAL 


55 


Table  5. — Value*  of  surface  and  of  coal  rights  by  counties  in  Illinois 


County 


Value  of  coal 
per  acre 


Number  of 
coal  bed 


Average 
surface  value, 
census  of  1910 


Bond    !         $  25 

Bureau     10-100 

Christian 10-50 

Franklin    35-100 

Fulton    15-100 

Gallatin   20-25 

Grundy    10-25 

Henry    135 

Jackson   25-  75 

La  Salle    10-100 

Livingston    10-  50 

Logan    20-50 

Macoupin    15-  50 

Madison    10-40 

Marion     20 

Marshall    15 

McLean   15 

Menard    25-30 

Montgomery    25-  50 

Morgan   20-30 

Peoria    20-50 

Perry   25 

Putnam    15 

Randolph    25 

St.  Clair 10-100 

Saline 50-150 

Sangamon     20-100 

Scott    10-  40 

Shelby    10-25 

Vermilion     100-150 

Warren    15 

Will    15 

Williamson     50-150 

Woodford     15 


6 

2 

6 

6 

5 

5 

2 

6 

2,6 

2,5 

6 

5 

6 

6 

6 

2 

5 

6 

6 

6 

5 

6 

2 

6 

6 

5 

5,6 

2 

6,5 

6,7 

1,2 

2 

6 

2 


$  45.43 

114.53 

123.63 

38.48 

88.18 

48.60 

72.52 

112.03 

31.27 

142.92 

161.76 

156.49 

69.74 

70.53 

39.45 

123.92 

171.85 

122.04 

73.49 

124.28 

107.67 

30.62 

104.69 

36.11 

81.57 

39.88 

138.30 

83.21 

88.72 

138.85 

129.80 

104.08 

30.61 

154.27 


*These  prices  are  not  offered  as  an  authoritative  basis  for  valuation  but  indicate  in 
a  general  manner  the  prices  at  which  coal  has  been  sold  or  at  which  it  is  held  in  some  of 
the   important   counties. 


run  coal  were  given  for  Illinois :  northern  Illinois,  5  cents ;  southern 
Illinois,  2  cents ;  La  Salle  district,  10  to  25  cents  per  ton  of  screened 
coal. 

In   1914,  the  leasing  rates  were  reported  in  various  counties  as 
follows  :     Franklin,  3  cents  ;  Fulton,  3  to  4  cents ;  Henry,  12^2  cents ; 


56 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


Jackson,  3  to  5  cents;  La  Salle,4  10  to  15  cents;  Peoria,  8  cents;  Perry, 
3  cents ;  Rock  Island,  20  cents ;  Vermilion,  3  cents ;  and  Williamson,  3 
cents. 

Table  5  shows  the  range  of  prices  for  coal  rights,  depending  upon 
the  proximity  to  operating  shafts  and  developed  lands. 

The  United  States  Geological  Survey5  gives  the  following  sale 
prices  for  1910:  Illinois,  $10-150;  Grundy  district,  $40-110;  Rock 
Island  district,  $50-75;  Springfield  district,  $10;  and  southern  Illinois, 
$25-50. 

In  response  to  an  inquiry  regarding  the  assessed  value  of  coal 
lands  in  Illinois  in  1913,  the  various  assessors  furnished  the  data  given 
in  the  accompanying  table. 


Table  6. — Assessed  valuation  of  coal  rights  and  of  agricultural  lands 

by  counties 


County 

Assessed  value  of 
coal  rights  in    1913 

ssed  valut 
arm  lands 

including 
rovements 

coal 

Remarks 

Highest 

Lowest 

Average 

Asse 
of  f 
not 
imp 
and 

Christian    .... 

$   5.00 

$  5.00 

$  5.00 

$77.18 

Includes    improvements,    but 

Fulton    

35.00 

35.00 

35.00 

60.00 

La  Salle 

7.00 

1.53 

4.89 

20.51 

Livingston     .  . 

10.00 

10.00 

10.00 

27.50 

Reduced  for   1914. 

Logan  

90.00 

Coal  rights  not  assessed. 

Madison     .... 

7.00 

7.00 

7.00 

22.00 

Menard    

7.00 

7.00 

7.00 

20.00 

Mercer   

18.00 

11.00 

14.50 

11.00 

Average  of  land  for  which  coal 
right   is   assessed    separately. 

Perry    . 

.... 

30  00 

Improved ;  coal  rights  not 
assessed. 

Putnam    

3  50-5.00 

Randolph  .... 

11.00 

8.00 

8.69 

23.46 

Full  value. 

St.  Clair 

60.00 

3.00 

25.00 

50.00 

Not  including  E.  St.   Louis. 

Saline   

10.00 

3.00 

6.00 

25.00 

Including    improvements. 

Scott   

Coal  rights  not  assessed. 

Washington    . 

5.00 

3.30 

3.80 

8  09 

NATURE    OF    DAMAGE    TO    AGRICULTURAL    LANDS 

As  previously  noted  the  removal  of  the  coal  may  cause   (1)   the 
caving  of  the  surface  with  the  formation  of  cracks  and  pit  holes;  (2) 


4In  the  La  Salle  district  most  of  the  coal  mined  is  owned  by  the  mining  companies, 
and  very  little  is  leased. 

"Ashley,  G.  H.,  Valuation  of  public  coal  lands:  U.  S.  Geol.  Survey  Bull.  424,  p. 
35,    1910. 


DAMAGE   BY   COAL   REMOVAL  57 

the  sagging  of  the  surface,  resulting  in  the  derangement  of  natural  and 
artificial  drainage;  (3)  the  fracturing  of  beds  containing  or  preserv- 
ing water  supply;  or  (4)  damage  to  surface  improvements.  With  the 
proper  care  on  the  part  of  the  mine  operator  some  of  these  damages 
may  be  prevented  or  reduced.     (See  Chapter  V.) 

In  the  main  it  may  be  said  that  damage  to  farm  property  is  only 
temporary,  and  the  land  and  property  can  be  restored.  On  the  other 
hand  when  a  portion  of  the  coal  is  left  in  the  ground  as  support  for 
the  surface,  it  is  irretrievably  lost,  at  least  according  to  our  commercial 
standards  of  the  present  time.  In  discussing  mining  wastes  in  Illinois, 
Mr.  G.  S.  Rice6  said : 

"If  it  were  possible  to  systematize  mining  (longwall)  so  that  the  land  near- 
est the  water  courses  was  first  undermined  and  then  in  succession  the  land  farther 
'away,  the  damage  done  to  farming  would  be  minimized.  However,  until  the 
agricultural  land  of  the  United  States  becomes  insufficient  to  fill  the  needs  of  the 
population,  which  would  be  reflected  in  a  continual  increase  of  price  for  farming 
land,  the  money  loss  from  temporarily  destroying  the  surface  in  places  is  rela- 
tively small  as  compared  with  the  selling  price  of  the  coal  mined  under  the 
same.  Taking  the  average  value  of  the  surface  at  $125.00  per  acre,  if  80  per 
cent  be  rendered  worthless,  the  immediate  money-loss  would  be  $100  per  acre. 
A  seam  6  feet  thick  would  contain  per  acre  11,000  tons  of  coal  in  place,  yielding 
at  90  per  cent,  9,900  tons.  The  damage  done  by  practically  destroying  the  sur- 
face would  be  only  1  cent  per  ton.  If  the  land  prices  should  rise  two  or  three 
times  above  the  value  stated,  this  loss  would  still  not  prohibit  mining." 

It  may  be  suggested  that  under  average  conditions  in  Illinois  at 
present  45  per  cent  of  the  coal  is  left  in  the  ground  in  certain  portions 
of  the  State  largely  to  prevent  surface  subsidence.  If  an  additional 
35  per  cent  were  recovered  and  damage  to  the  surface  should  thereby 
result  to  the  extent  suggested  by  Air.  Rice,  the  increased  output  per 
acre,  3,850  tons,  may  be  charged  with  the  surface  damage,  assuming 
that  ordinary  mining  costs  remain  the  same  (they  would  probably  be 
reduced)  with  the  increased  tonnage.  At  a  price  of  $125  per  acre,  the 
cost  per  ton  for  surface  damage  would  be  2.6  cents.  Many  mining  op- 
erators figure  on  this  basis,  and  their  experience  has  been  that  as  a 
rule  they  are  obliged  to  pay  damages  greatly  in  excess  of  the  actual 
depreciation  in  value  of  the  property. 

The  suggestion  has  been  made  frequently  that  the  mining  company 
should  purchase  the  surface  as  well  as  the  coal  right,  and  that  as  soon  as 
the  coal  has  been  mined  completely  under  each  tract  or  farm,  the  prop- 
erty should  be  restored  as  nearly  as  possible  and  sold.  Under  such 
conditions  the  surface  would  propably  be  as  valuable  when  restored 
after  the  coal  had  been  mined  as  when  first  purchased  The  income 
from  the  use   of   the   surface   for   agricultural   purposes   would  have 


"Rice,  G.  S.,  Mining  wastes  and  mining  costs  in   Illinois:   Til.   State   Geol.   Survey  Bull. 
14,   p.    218,    1909. 


58 


SURFACE    SUBSIDENCE    IN    ILLINOIS 


been  sufficient  to  pay  the  interest  on  the  money  invested  in  the  land. 
If  the  company  suffers  any  loss  through  the  depreciation  of  the 
surface  it  would  be  small  as  compared  with  the  damages  that  would 
be  paid  to  the  surface  owner  under  conditions  such  as  now  exist  in  the 
coal-mining  districts.7 

RESTORING    AGRICULTURAL    LANDS 

Where  the  removal  of  the  coal  causes  local  sags  or  depressions, 
water  may  accumulate  to  such  an  extent  that  artificial  drainage  must 
be  provided.  If  the  sags  are  of  small  area  the  problem  may  not  be 
particularly  difficult  or  expensive. 

Figure  34  shows  the  position  of  3  sinks  with  regard  to  the 


""1 GG  ODoooaaCj  dd  c3QDaQDDD,JQoaC 


f"  jnaao  o 


r»owr?nofV«nnfi 


innnnnnjin 


|Qrp 


ifl'J!  WitfnS 


2l)o^  t^iiaOaZiiia^lSufl/lfllliiLii 

-'  0  o  o  ■;:?,  o  o  ci  o  o  coi  !  L.I  r^o<:>f:K:^ooc-7c-jM=xa)     1  fl! 


Fig.  34. — Map  showing  location  of  tile  drains  laid  by  a  mining  company  to 
drain  sags  caused  by  mining  a  7-foot  coal  at  a  depth  of  330  feet. 


workings  of  a  room-and-pillar  mine.  At  a  depth  of  330  feet  a  7-foot 
coal  was  mined.  Rooms  were  carried  30  feet  wide  with  30-foot  pillars. 
The  floor  is  fire  clay,  and  it  is  thought  the  squeezes  were  due  largely 
to  the  soft  bottom.  In  order  to  remove  the  water  in  the  ponds  form- 
ed after  the  subsidence,  the  mining  company  laid  4,800  feet  of  tile  at 
a  cost  of  $647.57.  The  sags  were  from  2  to  3  feet  deep.  The  coal 
was  mined  from  3  to  5  years  before  the  subsidence  occurred. 


7Most   of    the    mining   companies   are   not    now 
amount   necessary   to   purchase   the    surface. 


a   position    to    invest   the   additional 


DAMAGE    BY    COAL    REMOVAL 


59 


At  a  longwall  mine  in  the  northern  part  of  the  State  it  was  found 
advisable  to  construct  a  sump  and  to  install  a  pumping  plant  in  order 
to  drain  a  pond  which  was  caused  by  surface  subsidence.  As  a  gen- 
eral rule,  it  is  found  more  economical  to  lay  drain  tile  at  possibly 
greater  first  cost. 

Where  breaks  or  pit  holes  result  from  mining  operations,  if  the 
surface  is  valuable,  it  will  usually  pay  to  fill  the  holes  partly  with  re- 
fuse and  then  to  surface  with  a  layer  of  soil  sufficiently  deep  to  support 
vegetation.  The  Agricultural  Department  of  the  University  of  Illinois 
recommends  that  the  soil  cover  should  be  not  less  than  4  feet  in 
depth.  If  the  soil  in  its  natural  state  is  less  than  4  feet  thick  over  the 
entire  area,  it  would  seem  equitable  to  make  the  soil  layer  of  the  filled 
area  of  equal  thickness  with  that  of  the  undisturbed  area. 


Fig.  35.— Pit  hole  filled  with  rubbish  at  the  Electric  mine  near  Danville. 


In  figure  35  is  shown  what  frequently  occurs  in  the  mining 
district — the  dumping  of  all  kinds  of  rubbish  into  the  cavities  without 
regard  to  the  ultimate  dressing  of  the  surface  with  soil.  Figure  36 
shows  the  practice  in  an  area  adjacent  to  Streator  where  the  holes  are 
filled  partly  with  mine  rock.  Figure  37  shows  a  field  near  Streator  in 
which  the  holes  have  been  filled  and  then  dressed  with  soil.  The  darker 
area  in  the  foreground  shows  the  fresh  filling.  The  hole  filled  was 
20  feet  in  diameter  and  averaged  about  6  feet  in  depth. 

Occasionally  a  subsided  area  extends  across  a  road.  In  many 
places  water  collects  and   forms  a  pond  that  extends  over  the  road. 


60 


SURFACE    SUBSIDENCE    IN    ILLINOIS 


In  order  to  make  the  road  passable  it  may  be  filled  to  grade  with  the 
material  most  easily  accessible. 

In  order  to  prevent  surface  water  from  entering  pit  holes  and 
thence  flowing  into  the  mine  below,  it  frequently  becomes  necessary 
to  construct  dikes  around  the  largest  holes  and  those  holes  located 


Fig.  36. — Pit  hole  and  cracks  caused  by  mining  at  a  shallow  depth  near 
Streator.  Mine  rock  near  the  hole  has  been  hauled  for  filling;  the  surface  will 
then  be  dressed  with  soil. 


Fig.  37. — Pit  holes  near   Streator  caused  by  room-and-pillar  mining  filled 
with  mine  rock  and  surfaced  with  soil.     The  dark  lines  border  the  area  of  filling. 

in  the  deepest  part  of  the  sags  or  in  the  course  of  the  drainage  of 
storm  water.  A  dike  3  feet  high  built  around  a  pit  hole  60  feet  in 
diameter  and  28  feet  deep  has  been  constructed  near  Dewmaine. 

It  may  be  stated  in  general  that,  except  where  the  "Coal  Measures" 
are  overlaid  with  thick  beds  of  quicksand  or  other  material  that  will  flow 


DAMAGE   BY    COAL   REMOVAL 


61 


easily,  there  will  be  little  irreparable  damage  to  the  surface  on  account 
of  coal-mining  operations,  particularly  when  the  coal  is  removed  com- 
pletely. If  a  considerable  portion  of  the  coal  is  left  permanently 
in  pillars,  the  surface  will  probably  be  thrown  into  hummocks  and  sags, 
with  occasional  breaks  and  ponds.  A  complete  removal  of  the  coal 
will  leave  the  surface  in  a  much  better  condition  for  farming  purposes. 
If  the  rock  cover  is  thin  and  the  overburden  has  a  tendency  to  flow  into 
the  mine,  special  precautions  must  be  taken  or  the  surface  will  be  con- 
siderably broken,  due  to  the  flow  of  sand  into  the  workings. 

At  present  attempts  at  filling  the  mine  workings  by  flushing  seem 
to  be  impracticable  for  the  greater  portion  of  the  Illinois  coal  fields 
owing  to  the  scarcity  of  material  suitable  for  filling.  If  surface 
material  is  taken,  a  considerable  area  will  be  rendered  unfit  for 
agricultural  purposes  due  to  the  removal  of  the  soil.  In  portions 
of  the  State,  however,  it  is  possible  that  in  the  future  market  con- 
ditions may  warrant  higher  mining  costs,  and  under  such  conditions 
hydraulic  stowing  of  crushed  material  from  surface  quarries  may 
be  feasible. 

Transportation  and  Surface  Subsidence 
railroads 

The  practice  of  separating  the  mining  right  from  the  title  to  the 
surface  has  frequently  resulted  in  mining  beneath  roads,  streets,  and 
railroads  without  any  consideration  of  the  protection  of  the  surface. 
In  many  instances  the  deed  for  the  mining  rights  specifies  that  the 
coal  may  be  removed  completely  and  without  a  liability  for  damage 
to  the  surface.  In  other  instances  in  which  damage  to  the  surface  has 
resulted,  an  effort  has  been  made  to  remove  as  large  a  portion 
of  the  coal  as  possible  without  injury  to  the  surface.  Certain  rail- 
roads have  permitted  mine  entries  to  be  driven  across  the  right-of- 
way  and  have  forbidden  the  opening  of  rooms  within  a  specified 
distance  of  the  center  of  the  track.  In  several  cases  mining  has 
been  carried  on  according  to  the  regulation  of  the  railroad,  but  the 
removal  of  coal  outside  the  reserved  area  has  resulted  in  "draw" 
or  "pull"  which  has  threatened  the  railway  tracks.  Railways  have 
been  constructed  across  tracts  which  have  previously  been  under- 
mined by  the  room-and-pillar  system  and  on  which  no  subsidence 
has  occurred.  In  time  the  pillars  have  weakened,  and  the  added 
burden  and  the  vibration  due  to  the  passing  trains  have  resulted  in 
the  sinking  of  the  tracks.  In  the  opinion  of  a  number  of  experienced 
railroad   engineers  the  problem   of   subsidence   as   affecting  railroads 


62  SURFACE    SUBSIDENCE    IN    ILLINOIS 

is  much  different  from  that  affecting  other  types  of  property,  due 
principally  to  the  intermittent  and  moving  loads. 

Few  instances  have  been  recorded  in  Illinois  of  the  loss  of  life 
or  injury  to  patrons  or  employes  of  railroads  resulting  directly  from 
subsidence  due  to  mining  beneath  the  right-of-way. 

Figure  38  shows  the  partially  regraded  railway  track  over  a 
mine  in  which  9  feet  of  coal  has  been  worked  at  a  depth  of  425  feet. 
In  the  distance  the  work  train  can  be  seen  as  filling  material  is  being 


';:■ 


,..■■■..*■'■■ 


*    **         1j  *0h>M**.±^_*m- 


Fig.  38.— Railroad  track  in  Franklin  County  lowered  by  surface  subsidence 
resulting  from  room-and-pillar  mining  of  a  9-foot  coal  at  a  depth  of  425  feet. 
The  maximum  subsidence  was  4  feet.     The  track  has  been  partially  repaired. 

unloaded  for  the  regrading  of  a  switch.  Figure  39  shows  the  nature 
and  extent  of  the  workings  beneath  the  surface  tracks  which  have 
subsided.  The  rooms  were  carried  30  feet  wide  by  300  feet  long; 
pillars  were  20  feet  wide.  The  squeeze  covered  an  area  1,200  feet 
square,  and  the  depression  at  the  surface  was  in  places  4  feet.  The 
underclay  is  quite  soft  in  parts  of  the  mine. 

One  of  the  large  railroad  companies  reports  that  in  the  La  Salle 
district  it  has  been  necessary  to  raise  and  surface  the  main  line 
track  every  year,  the  total  subsidence  being  estimated  at  about  3 
feet.  It  is  reported  by  two  railroad  companies  that  subsidence  result- 
ing from  longwall  mining  in  the  vicinity  of  Decatur  has  necessitated 
regrading  and  filling  amounting  to  3  to  4  feet. 

Room-and-pillar  mining  in  southern  Illinois  has  caused  consider- 
able damage  to  railroad  tracks.     Near  Duquoin  a  track  to  a  mine 


DAMAGE    BY    COAL    REMOVAL 


63 


subsided  3  feet.  A  branch  line  of  a  railroad  in  Williamson  County 
was  damaged  by  a  sink  hole  6  feet  in  diameter  and  20  feet  deep.  This 
occurred  over  the  abandoned  workings  of  a  mine  90  feet  deep.  Im- 
portant tracks  have  subsided  amounts  varying  from  a  few  inches  to 
a  few  feet  at  numerous  places.     Important  bridges  have  been  threat- 


'             V         * 

J     1        1    \ 

;    /•")      r^:~j  fo_o  r— — - ;  r: 

V      /'   _           "\      ' 

i       i  ■     ;  '  ■*-'"!  / 

i        i  '-.-_<    ■'          i   ; 

-               !  — -_/     v..           rt 

'      — ">     '*_''                                                           o 
1    *        '     r — -^ «        — 

.  /    !  n  P~- ~>  ^— 1 17 

;    J       {     j                  ;   (                 j    \J 

i     !     !     !          /  /            ,;  (    J  L''    l« 
J     - —     « <•- - 

<- 'i    j  j           _   }  I          i  O1  {u/ 

/->  ',    i    ;'              )  (      ,J  N 

r  !  ;    S    :        !  i       !  i 

>:/  U  p—  f— If- 1  r~ 

i                      /I 
I                / 

I      $ 

i 

1 
i 

1 
1 

. (  . 

,__n ^ 

Scale  1  inch  =  200  feet 
Fig.  39.— Plan  showing  relation  of  railroad  in  figure  38  to  mine  workings. 


ened;  one  pier  of  a  bridge  is  reported  to  have  subsided   18  inches 
but  without  much  tilting  (fig.  40). 

It  is  now  the  practice  of  the  railroad  companies  whose  lines 
extend  through  mining  districts  to  secure  annually  from  their  division 
engineers  complete  reports  showing  the  extent  of  mining  beneath 
the  right-of-way. 


64 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


WAGON    ROADS 

Generally  the  title  to  the  coal  beneath  wagon  roads  is  not  reserv- 
ed by  the  district  maintaining  the  roads.  Frequently  where  there  is 
a  likelihood  that  the  roads  may  be  damaged  by  mining  operations 
an  agreement  exists  between  the  mining  company  and  the  local  officers 
to  the  effect  that  any  damage  to  any  road  will  be  repaired  by  and  at 
the  expense  of  the  mining  company. 

In  the  Longwall  District  of  northern  Illinois  a  general  subsidence 
following  the  advance  of  the  longwall  face  in  many  places  results 
in  the  inundation  of  the  roads  during  part  of  the  year.     At  a  number 


Fig.  40. — Repaired  railroad  trestle  in  Franklin  County.  One  end  subsided 
18  inches  more  than  the  other,  the  total  having  been  reported  as  about  4  feet. 
Timbers  were  placed  at  A,  B,  C,  and  D  in  order  to  reduce  the  sag  of  the  track 
over  the  trestle. 

of  places  the  mining  companies  responsible  for  the  subsidence  have 
constructed  adequate  ditches  paralleling  the  sunken  road  in  order 
to  remove  the  water.  It  is  not  uncommon  for  the  mining  companies, 
as  important  users  of  the  roads,  to  haul  mine  refuse  and  ashes  to 
fill  the  road  to  the  desired  grade. 


STREAMS   AND    CANALS 

Mining  has  been  carried  on  beneath  several  navigable  streams 
and  canals,  but  in  no  instance  has  the  water  been  let  into  the  mine, 
nor  has  subsidence  caused  any  appreciable  damage  to  the  water  course 


DAMAGE   BY    COAL   REMOVAL 


65 


— at  least  not  to  the  extent  of  interfering  with  its  usefulness  for  the 
passage  of  watercraft. 

Buildings  and  Improvements  Affected  by  Subsidence 

buildings 

The  subsidence  of  the  surface  over  a  large  area  may  be  so 
uniform  and  so  gradual  as  to  cause  no  serious  damage.  In  parts 
of  the  longwall  field  mining  has  been  reported  to  have  had  no  appreci- 
able effect  upon  the  frame  buildings  at  the  surface.  The  effect 
is  less  if  the  mining  face  advances  rapidly  and  across  the  shorter 
axis  of  the  building.  As  previously  noted,  the  building  is  in  a  ten- 
sion zone  as  the  mining  face  approaches  and  passes  under  the  building, 
and  the  section  of  the  building  under  which  the  coal  has  been  removed 
first  tends  to  tilt  toward  the  mine  and  to  tear  itself  free  from  the 
remainder  of  the  building.     If  the  building  is  constructed  of  masonry, 


Fig.  41. — House  near  Coal  City  lowered  9  inches  at  one  corner,  caused  by 
mining  a  3-foot  coal  at  a  depth  of  125  feet. 

serious  cracks  may  form  and  afterward  close  when  the  mining  face 
has  advanced  completely  beyond  the  building. 

When  the  advance  of  longwall  mining  has  been  stopped  under 
or  adjacent  to  a  building,  the  surface  is  likely  to  be  tilted  enough 
to  throw  the  building  out  of  plumb.  Figure  41  shows  a  house  in 
the  Coal  City  district  which  was  thrown  out  of  plumb  by  the  stop- 
ping of  the  longwall  face  near  the  house.  The  coal  beneath  had  not 
been  mined.  The  seam  of  coal  is  3  feet  thick  and  lies  at  a  depth  of 
125  feet.  One  corner  of  the  house  was  almost  one  foot  lower  than  the 
other  corners. 


66 


SURFACE    SUBSIDENCE    IN    ILLINOIS 


The  removal  of  part  of  the  coal  by  room-and-pillar  mining  is 
more  likely  to  damage  buildings  seriously  than  is  the  complete  removal 
of  the  coal  by  the  longwall  system.  This  difference  results  from 
the  probable  formation  of  pits  and  from  the  unequal  subsidence  that 
may  tear  to  pieces  a  building  that  happens  to  be  located  over  a  pillar. 
If  it  is  located  in  the  middle  of  a  small  sag,  the  compression  or 
squeezing  may  be  so  great  as  to  destroy  the  building. 

Figure  42  shows  the  part  of  a  brick  house  still  standing  above 
a  pillar  in  a  mine  near  Danville.  Approximately  6  feet  of  coal  was 
taken  out  at  a  depth  of  200  feet,  The  position  of  the  house  with 
regard  to  the  mine  workings  is  shown  in  figure  43. 


Fig.   42. — Brick  house   near   Danville  abandoned  on   account  of  danger  by 
room-and-pillar  mining  of  a  6-foot  coal  at  a  depth  of  about  200  feet. 


Figure  44  shows  a  portion  of  a  row  of  houses  in  Springfield 
These  brick  houses  were  damaged  by  subsidence  resulting  from  room- 
and-pillar  mining.  The  coal  is  5  feet  9  inches  thick  and  lies  at  a 
depth  of  approximately  200  feet.  A  pillar  10  feet  wide  was  left 
along  the  street  and  this  apparently  was  responsible  for  the  crack- 
ing of  the  houses.  If  all  the  coal  had  been  removed  the  houses 
probably  would  have  settled  uniformly.  The  houses  have  been  re- 
paired at  the  expense  of  the  mining  company. 

In  figure  45  is  shown  a  small  frame  house  in  the  suburbs  of 
Streator.  A  pit  hole  10  by  20  feet  and  5  feet  deep  has  been  formed 
along  one  side  of  the  house. 

In  southern  Illinois  has  recently  occurred  a  movement  affecting 
a   large   area   in  one   of   the  coal-mining  towns.    Eight   feet  of   coal 


DAMAGE    BY    COAL   REMOVAL 


67 


was  being  mined  by  the  room-and-pillar  method  at  a  depth  of  ap- 
proximately 450  feet.  Rooms  were  carried  30  feet  wide  with  15-foot 
pillars.  Figure  46  gives  a  general  view  showing  the  flooded  streets 
resulting  from  the  subsidence.  The  maximum  depth  of  the  sag  was 
about   3   feet.     The    foundations   of   houses   were   cracked,   and   in   a 


~---_                          -J 

?  / — ^    -1 

r 
i 

i 

L. 

/ 

1       ! 

i 

i 

"-V->W-^J 

i 

i 
i 

1 
I 

i 

/ 

i 

/     v>.v-             ^s      i 

-J 

" 

'       i           "~""~~-*-.^*---      — -j 

f> 

N 

1 

N 


"I    L- 


i  n 

i   j 

1  i ! 


n1 


,--1 


LJ  i      V 


'  L- 
i 

i  „- 

J  l 


Scale  1  inch  =  200  feet 
Fig.  43. — Plan  showing  relation  of  house  in  figure  42  to  the  pillar  in  the 


number  of  houses  the  plaster  fell.  Another  depression  at  the  same 
mine  resulted  in  lowering  one  end  of  the  company  barn  over  4  feet. 
The  barn  has  been  repaired,  but  one  end  is  still  approximately  15 
inches  lower  than  the  other.  The  tilting  of  the  barn  is  shown  in 
figure  47. 


68 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


FIG_  44.— Houses  in  northwest  Springfield  for  which  claims  were  paid  by 
a  mining  company  for  damages  caused  by  mining  a  coal  5  feet  9  inches  thick  at 
a  depth  of  about  200   feet. 


.'-.'     ••*•<<.  i  .  <*:... 


IB 


Fig.  45.— Small  house  near  Streator  beside  which  a  pit  hole  10  by  20  feet 
and  5  feet  deep  has  formed. 


DAMAGE  BY   COAL   REMOVAL 


69 


STREETS,    PIPE    LINES,    AND    SEWERS 

Mining  within  the  limits  of  cities  and  towns  and  the  construction 
of  towns  upon  lands  which  have  previously  been  undermined  have 
been  attended  with  more  or  less  danger  owing  to  the  subsidence  of  the 
streets.     Where  coal  at  shallow  depth  has  been  mined  by  the  room-and- 


Fig.  46. — Flooded  streets,  broken  sidewalks  and  foundations,  and  damages 
to  plastering  resulting  from  subsidence  in  Franklin  County.  Figure  48  shows 
the  broken  sidewalk  at  A.     (Photo  by  H.  T.  Smith,  U.  S.  Bureau  of  Mines.) 


\      /. 


Fig.  47. — Barn  of  mining  company  lowered  4  feet  at  one  end. 
partially  restored. 


It  has  been 


pillar  system,  a  sudden  collapse  of  the  overlying  beds  into  the  worked- 
out  rooms  may  result.  Passing  teams  have  at  several  times  been 
reported  to  have  dropped  with  the  surface  into  a  pit  hole.  No  fatal 
accidents  are  known.  Where  the  coal  is  at  greater  depth,  or  where 
the  coal  has  been  mined  by  the  longwall  system,  the  movement  will 


70 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


probably  not  be  attended  by  the  formation  of  holes  into  which  build- 
ings or  creatures  may  fall. 

The  gradual  sinking  of  the  surface  may  do  serious  injury  to 
pavements,  sidewalks,  car  tracks,  pipe  lines,  and  sewers.  Numerous 
instances  of  such  damage  have  been  reported  but  as  repairs  are  usually 
made  immediately  there  has  been  little  opportunity  to  secure  photo- 
graphs illustrating  this  type  of  damage. 

Figure  48  shows  a  broken  sidewalk  caused  by  subsidence.  Mining 
was  being  carried  on  by  the  room-and-pillar  method  at  a  depth  of 
450  feet  on  an  8-foot  seam  of  coal. 


g.  48.— Broken   sidewalk  caused  by   subsidence   in   Franklin   County;  the 
location  is  shown  in  figure  46.     (Photo  by  H.  I.  Smith,  U.  S.  Bureau  of  Mines.) 

In  order  to  secure  reliable  information  regarding  the  extent  of 
mining  operations  within  the  towns  of  the  State,  and  the  nature  and 
amount  of  damage  which  has  been  attributed  to  mining,  a  general  letter 
was  sent  in  August,  1914,  to  the  mayor  of  each  of  80  more  or  less 
typical  incorporated  towns  and  cities  in  the  coal  districts.  Replies8 
were  received  from  56. 


8The  towns  reporting  were  Auburn,  Belleville,  Bloomington,  Braidwood,  Breese,  Car- 
bondale,  Carterville,  Christopher,  Colchester,  Coulterville,  Duquoin,  Edinburg,  Fairbury, 
Farmington,  Galesburg,  Geneseo,  Ilarrisburg,  Hillsboro,  Jacksonville,  Kewanee,  Lewistown, 
Lincoln,  Litchfield,  Lovington,  Macomb,  Marion,  Marissa,  Mascoutah,  Mattoon,  Minonk, 
Morris,  Mount  Olive,  Moweaqua,  Murphysboro,  Nashville,  Nokomis,  Norris  City,  Odin, 
O'Fallon,  Pana,  Peoria,  Peru,  Pinckneyville,  Pontiac,  Riverton,  Salem,  Seneca,  Shelbyville, 
Sorento,   Springfield,   Spring  Valley,   Staunton,   Streator,   Virden,   West   Frankfort,   and  Witt. 


DAMAGE    BY    COAL   REMOVAL  71 

The  questions  and  answers  were  as  follows: 

1.  Has  coal   ever  been  mined  within  the  city  limits?     Yes,   in  48  towns 

of  56  replying. 

2.  Has   coal   ever  been  mined   under  the  streets  and   alleys?     Yes,   in  39 

towns  of  56  replying. 

3.  Has  any  damage  resulted  to  the  streets  and  alleys  on  account  of  the 

mining  of  the  coal?     Yes,  in  5  towns  of  56  replying;  no,  in  49. 

4.  Does  the  city  now  own  or  control  the  right  to  mine  coal  under  any  or  all 

of  the  streets  and  alleys?     Yes,  in  17  of  56  replying;  no,  in  35. 

The  replies  to  question  No.  3  received  from  the  five  cities  and 
towns  reporting  damage  to  streets  and  alleys  were  as  follows: 

1.  Yes. 

2.  Not  recently,  but  in  former  years  some  subsidences  caused  some  trou- 

ble.    These  have  been  fixed  except  one  that  gives  some  trouble,  but 
nothing  serious. 

3.  A  little. 

4.  Some  cave-ins. 

5.  Yes.     Sink  on   North   Main   Street  and  property  adjoining  it;   also  in 

east  and  west  part  of  city. 

The  mayor  of  one  town  in  which  a  7-foot  seam  of  coal  lies  at  a 
depth   of   less   than   450   feet   reports   that   "the   city   has   deeded  the 

right  to  mine  coal  under  all  its  streets  to  the Coal  Company, 

and  they  have  been  mined  as  far  as  Main  Street."  The  coal  company 
reports  that  50  per  cent  of  the  coal  is  left  unmined,  the  rooms  being 
from  30  to  35  feet  wide  on  55-foot  centers.  The  mining  company 
has  not  been  released  from  surface  damage.  There  has  recently 
occurred  in  this  town  a  movement  which  damaged  a  railroad  right-of- 
way. 

Another  mayor  wrote  as  follows  :  "The  right  to  mine  coal  under 
streets  and  alleys  was  voted  to  -  -  Coal  Company  several  years 

ago."  At  this  place  the  coal  is  7  feet  thick  and  is  over  600  feet  below 
the  surface. 

A  city  in  the  Longwall  District  of  northern  Illinois  receives  a 
yearly  rental  for  the  privilege  of  mining  coal  under  the  streets.  A 
city  ordinance  granted  this  privilege  conditional  upon  the  payment 
of  the  rental. 

WATER    SUPPLY 

At  a  number  of  places  in  the  State  it  has  been  reported  that 
wells  have  ceased  to  furnish  the  usual  supply  of  water  owing  to  the 
cracks  and  fissures  resulting  from  subsidence.  In  some  instances 
water-bearing  rocks  have  been  shattered,  and  in  others  gravel  beds 
and  catchment  basins  have  been   tilted  or  disturbed  so  that  they  no 


72  SURFACE    SUBSIDENCE   IN    ILLINOIS 

longer  serve  as  reservoirs  for  water.  However,  in  a  number  of  in- 
stances after  the  subsidence  movement  has  stopped,  the  surficial 
beds  have  become  compact  and  have  again  furnished  water  in  quantities 
nearly,  if  not  quite,  as  great  as  previously. 

MUNICIPAL    WATERWORKS 

The  protection  of  city  waterworks  is  a  matter  which  merits 
serious  attention.  At  several  points,  notably  at  two  cities  of  over  50,000 
population,  mine  workings  are  advancing  toward  the  waterworks. 
In  these  two  large  cities  the  undermining  of  the  wells,  reservoirs,  and 
plants  will  cause  serious  damage. 

Reservations  of  Coal 

The  topic  of  reservations  may  logically  be  considered  under  the 
discussion  of  protection  of  the  surface  and  directly  in  connection 
with  pillars.  It  has  been  more  or  less  customary  for  the  owners 
of  farm  lands  when  selling  the  coal  right  to  reserve  a  tract  of 
the  coal  under  the  dwelling,  the  well  and  cistern,  the  barn,  and  any 
important  farm  buildings  adjacent  to  the  dwelling.  The  advisability  of 
leaving  a  small  tract  of  coal  for  the  protection  of  the  surface  is  seriously 
questioned.  If  the  coal  is  not  thick  and  can  be  removed  rapidly  and 
completely  it  may  be  much  more  economical  to  have  the  coal  tak- 
en out  and  to  make  such  minor  repairs  as  may  result  from  subsidence. 
The  presence  of  faults  and  beds  of  quicksand  would  complicate  matters. 

Moreover  under  some  conditions  the  angle  of  draw  may  be  so  great 
that  for  the  depth  at  which  the  coal  occurs  the  size  of  reservation 
necessary  for  adequate  protection  would  be  entirely  out  of  proportion 
to  the  value  of  the  objects  on  the  surface  for  which  protection  is 
desired. 

There  are  no  statutes  in  Illinois  forbidding  mining  under  any 
particular  type  of  structures,  public  utilities,  or  other  buildings,  al- 
though there  are  such  statutes  in  some  states.  When  it  can  be  shown 
that  irremediable  damage  would  result  to  property  used  for  public 
purposes,  or  when  mining  might  seriously  threaten  life  through  damage 
to  property  used  for  a  public  purpose,  an  injunction  may  be  secured 
restraining  mining  in  the  area  where  subsidence  is  feared. 


CHAPTER  IV— SUBSIDENCE  DATA  BY  DISTRICTS 
Introductory  Statement 

As  the  reports  upon  the  mining  practice  and  upon  the  geology  have 
assembled  the  data  by  districts,  it  has  been  thought  advisable  to  review 
the  data  on  subsidence  by  districts  so  that  they  may  be  correlated  with 
the  geological  and  mining  data. 

The  location  of  the  various  districts  is  shown  in  figure  49.  Table 
7  gives  the  districts  of  the  State  by  counties  and  Table  8  gives  the 
counties  arranged  alphabetically. 

Table  7.— Districts  into  which  the  State  has  been  divided  for  the  purpose  of 

investigation 


Coal 


Method  of 
mining 


Counties 


I 

II 
III 


IV 

V 
VI 

VII 


2 
1  and  2 


6  (East  of 
Duqtioin  anti- 
cline) 

6  (West  of 
Duquoin  anti- 
cline) 

6  and  7 
(Danville) 


Longwall 

Room-and-pillar 
Room-and-pillar 


Room-and-pillar 

Room-and-pillar 
Room-and-pillar 

Room-and-pillar 
Room-and-pillar 


Bureau,  Grundy,  La  Salle,  Marshall, 
Putnam,  Will,  Woodford. 

Jackson. 

Brown,  Calhoun,  Cass,  Fulton,  Greene, 
Hancock,  Henry,  Jersey,  Knox,  Mc- 
Donough,  Mercer,  Morgan,  Rock  Is- 
land, Schuyler,  Scott,  Warren. 

Cass,  DeWitt,  Fulton,  Knox,  Logan, 
Macon,  Mason,  McLean,  Menard,  Peo- 
ria, Sangamon,  Schuyler,  Tazewell, 
Woodford. 

Gallatin,  Saline. 

Franklin,  Jackson,  Perry,  Williamson. 


Bond,  Christian,  Clinton,  Macoupin, 
Madison,  Marion,  Montgomery,  Moul- 
trie, Perry,  Randolph,  Sangamon,  Shel- 
by, St.  Clair,  Washington. 

Edgar,  Vermilion. 


(73) 


utiles 


Fig.  49. — Map  showing  division  of  State  into  districts. 


SUBSIDENCE   DATA 


75 


Table  8. — Alphabetical   arrangement   of   coal-producing   counties 


County 


Bond  . . . 
Brown    . 
Bureau  . 
Calhoun 
Cass    . . . 
Christian 
Clinton  . 
Edgar  . . 
Franklin 
Fulton    . 
Gallatin 
Greene   . 
Grundy 
Hancock 
Henry  . .  , 
Jackson    . 
Jersey  .  .  . 
Knox    . . . 
La    Salle. 
Logan  .  .  . 
Macon    .  . 
Mason    . . 
Macoupin 
Madison 
Marion  .  . 


Coal  seam 


District 


6 

2 
2 
2 

2,5 

6 

6 
6,7 

6 
1,2,5 

5 
1,2 

2 
1,2 
1,2 
2,6 
1,2 

5 

2 

5 

5 

5 

6 

6 

6 


VII 

III 

I 

III 

III,  IV 

VII 

VII 

VIII 

VII 

III,  IV 

V 

III 

I 

III 

III 

II,  VI 

III 

IV 

I 

IV 

IV 

IV 

VII 

VII 

VII 


County 


Marshall  . .  . 
McDonough 
McLean  . . . 
Menard    .... 

Mercer 

Montgomery 
Moultrie    . . . 

Peoria    

Perry   

Putnam    

Randolph  . . . 
Rock  Island. 
St.  Clair  .... 

Saline 

Sangamon  .  . 
Schuyler    .  .  . 

Scott 

Shelby    

Tazewell  . . . 
Vermilion   . . , 

Warren    

Washington    . 

Will    

Williamson  .  , 
Woodford  .  .  . 


Coal  seam 

District 

2 

I 

1,2 

III 

5 

IV 

5 

IV 

1,2 

III 

6 

VII 

6 

VII 

5 

IV 

6 

VI,  VII 

2 

I 

6 

VII 

1,2 

III 

6 

VII 

5 

V 

5,6 

IV,  VII 

1,2,5 

111,1V 

1,2 

III 

6 

VII 

5 

IV 

6,7 

VIII 

1,2 

III 

6 

VII 

2 

I 

6 

VI 

2,5 

I,  IV 

These  districts  do  not  contain  quite  all  the  mines  operating  in  Illi- 
nois because  there  are  a  few  which  do  not  fall  into  the  arrangement 
such  as  the  Assumption  mine,  1004  feet  deep,  operating  in  coal  No.  1  at 
Assumption  in  Christian  County  and  a  few  small  room-and-pillar  mines 
in  coal  No.  2  in  the  longwall  held.  From  the  mines  included  in  the 
eight  districts  of  the  Coal  Mining  Investigations,  however,  there  is 
produced  98.3  per  cent  of  the  tonnage  of  the  State,  and  97.6  per  cent 
of  all  the  employes  in  coal  mines  in   Illinois  work  in  these  districts. 


District  I 

Practically  all  the  longwall  mines  of  the  State  are  included  in 
District  I.  In  Table  9  is  given  a  list  of  longwall  mines  arranged  ac- 
cording to  depth  and  showing  the  average  thickness  of  coal  worked. 
It  will  be  noted  that  the  majority  of  the  mines  are  being  worked 
through  shafts  more  than  300  feet  deep.  Of  the  36  shafts  only  2 
are  more  than  600  feet  deep,  and  these  are  outside  of  the  longwall 
district  proper. 


76 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


Reference  has  previously  been  made  to  the  character  of  roof  and 
floor  in  District  I.  Attention  may  be  called  again  to  the  extension 
over  a  part  of  the  district  of  a  heavy  bed  of  limestone  25  to  30  feet 
thick  and  lying  375  to  400  feet  above  coal  No.  2  and  175  feet  above 
coal  No.  7.  Data  are  not  available  to  show  to  what  extent  this  bed 
influences  the  surface  movement  resulting  from  longwall  mining,  but 
it  is  reported  that  where  the  limestone  bed  is  known  to  occur,  the 
sinking  of  the  surface  does  not  follow  so  soon  after  the  coal  has  been 
removed  as  in  those  areas  where  the  limestone  is  known  to  be  missing 

Table   9. — Longwall  mines   in  Illinois 


Post  office 

rt*o 

<4-     0 

(/) 

Operator  and  mine 

address  of  mine 

O  u 

"oIj  <u 

ss 

y  m 

&3H 

g"8 

Feet 

Ft.  in. 

1.  Murphy,  Linskey  &  Kasher 

Braidwood 

2 

61 

3      3 

2.  Wilm.  C.  Mg.  &  Mfg.  Co.,  No.  6 

Torino 

2 

100 

3      6 

3.  Big  Four  Wilm.  C.  Co. 

Coal  City 

2 

100 

3      4 

4.  Wilm.-Star  Mg.  Co.,  No.  7 

Coal  City 

2 

126 

3     .. 

5.  G.  &  J.  Coal  Co.,  No.  1 

Seneca 

2 

130 

3     .. 

6.  Fulton  Co.  C.  Mg.  Co.,  No.  1 

Sparland 

2 

165 

2      8 

7.  Chic.  Wilm.  &  Fr.  Coal  Co.,  No.  1 

S.  Wilmington 

2 

186 

3      2 

8.  Chic.  Wilm.  &  Fr.  Coal  Co.,  No.  3 

S.  Wilmington 

2 

187 

3      2 

9.  111.  Zinc  Co.,  No.  3 

Peru 

2 

336 

3      6 

10.  Spring  Valley  Coal  Co.,  No.  1 

Spring  Valley 

2 

339 

3      4 

11.  111.  Zinc  Co.,  No.  1 

Deer  Park 

2 

364 

3      3 

12.  La  Salle  Co.  Carbon  Coal  Co. 

La  Salle 

2 

390 

3      4 

13.  Spring  Valley  C.  Co.,  No.  4 

Seatonville 

2 

393 

3      4 

14.  Spring  Valley  C.  Co.,  No.  5 

Dalzell 

2 

421 

3      4 

15.  La  Salle  Co.  Carbon  C.  Co.,  No.  1 

La   Salle 

2 

440 

3      4 

16.  Spring  Valley  C.  Co.,  No.  3 

Spring  Valley 

2 

457 

3      4 

17.  Oglesby  C.  Co. 

Oglesby 

2 

464 

3      6 

18.  111.  Third  Vein  C.  Co. 

Ladd 

2 

468 

3      6 

19.  Roanoke  C.  Co. 

Roanoke 

2 

480 

2      8 

20.  St.  Paul  C.  Co.,  No.  2 

Cherry 

2 

485 

3      6 

21.  St.  Paul  C.  Co.,  No.  1 

Granville 

2 

486 

3     .. 

22.  B.  F.  Berry  C.  Co.,  No.  1 

Granville 

2 

505 

3     .. 

23.  Rutland  C.  Co.,  No.  1 

Rutland 

2 

511 

2    10 

24.  Toluca  C.  Co.,  No.  1 

Toluca 

2 

512 

2     10 

25.  McLean  Co.  C.  Co. 

Bloomington 

2 

525 

3      6 

26.  LaSalle  Co.  Carbon  C.  Co.,  No.  5 

La  Salle 

2 

545 

3      6 

27.  Minonk  C.  Co.,  No.  2 

Minonk 

2 

550 

2      8 

28.  Mfrs.  &  Consumers  C.  Co. 

Decatur 

5 

560 

4      6 

29.  Decatur  C.  Co.,  No.  2 

Decatur 

5 

612 

4      6 

30.  Assumption  C.  Mg.  Co. 

Assumption 

1&2 

1004 

4     .. 

SUBSIDENCE  DATA  77 

and  where  there  is  the  same  total  thickness  of  overlying  sedimentary 
rocks. 

Data  from  10  shafts  ranging  from  50  to  550  feet  in  depth  showed 
the  average  subsidence  as  follows  in  percentage  of  thickness  of  the 
coal  mined : 

Depths  up  to  200  feet,  subsidence  averaged  55  per  cent. 
Depths  from  200  to  400  feet,  subsidence  averaged  50  per  cent. 
Depths  from  400  to  550  feet,  subsidence  averaged  39  per  cent. 
Sufficient  data  are  not  available  to  warrant  the  use  of  the  foregoing 
figures  as  the  basis  of  estimates  of  general  subsidence  in  the  Longwall 
District. 

For  all  depths  the  amount  of  subsidence  depends  largely  upon  the 
quality  and  quantity  of  material  stowed  in  the  gob.  It  should  be  ob- 
served that  as  the  depth  increases,  the  weight  of  the  overlying  rock 
increases  in  proportion,  and  the  material  in  the  gob  in  deeper  mines 
would  probably  be  compressed  more  than  the  gob  in  shallower 
mines.  With  the  same  quality  and  quantity  of  material  in  the  gob, 
all  other  underground  conditions  being  the  same,  there  may  be  as 
great  a  vertical  movement  of  the  surface  when  coal  is  mined  at  600 
feet  as  when  the  same  thickness  is  mined  at  200  feet.  Some  companies 
do  not  report  that  subsidence  has  occurred  at  their  mines,  and  some 
question  whether  it  actually  occurs  on  their  property.  This  probably 
is  an  honest  statement  resulting  from  the  lack  of  established  monu- 
ments and  the  failure  to  take  elevations  from  time  to  time  to  show 
actual  changes  in  the  surface.  In  the  greater  part  of  the  district, 
however,  it  is  generally  acknowledged  that  some  subsidence  results, 
but  it  is  claimed  that  the  surface  movement  is  inappreciable  in  most 
places  and  does  not  cause  damage  to  property  on  the  surface. 

As  previously  noted  one  of  the  most  common  forms  of  damage 
is  by  the  flooding  of  lands  by  creation  of  sags  or  the  sinking  of  areas 
below  the  previous  drainage  channels  or  flood  plains  (see  figure  24). 
Some  damage  to  buildings  has  been  done  but  only  little  has  been 
serious  (see  figure  41).  Brick  buildings  have  suffered  more  than 
frame  buildings.  No  brick  building  has  been  irremediably  damaged. 
Foundations  have  been  cracked,  but  where  all  the  coal  has  been  removed 
and  the  longwall  face  has  advanced  well  beyond  the  structure,  the 
cracks  have  partly  closed.  Several  long  buildings  have  been  badly 
cracked  when  the  longwall  face  has  not  been  advanced  rapidly  as 
the  coal  beneath  the  building  was  being  removed.  In  three  towns 
the  occasional  trouble  with  water  and  gas  mains  is  attributed  to 
subsidence  resulting  from  mining. 

In  this  district,  one  of  the  oldest  mining  districts  in  the  State, 
there  have  been  relatively  few  lawsuits  on  account  of  surface  damage 
resulting    from    subsidence.     Most   of   the   claims    for   damages   have 


78  SURFACE    SUBSIDENCE   IN    ILLINOIS 

arisen  on  account  of   the   flooding  of  lands,  and  these  have  usually 
been  adjusted  out  of  court. 

District  II 

This  district  comprises  Jackson  County.  The  commercial  coals 
lie  at  shallow  depths,  the  deepest  shaft  being  165  feet.  The  coal 
varies  in  thickness  from  3  feet  6  inches  to  9  feet,  and  one  small 
mine  is  operated  on  a  bed  12  feet  thick.  All  the  mining  is  done 
on  the  room-and-pillar  plan.  The  percentage  of  coal  recovered,  as 
reported  for  four  representative  mines,  ranges  from  44  to  55,  the 
average  being  48.5.  Due  to  a  thin  cover  over  a  large  territory  and 
considerable  sand  in  the  surface  beds,  a  great  deal  of  damage  to  the 
surface  has  occurred  in  certain  areas.  It  may  be  said  that  in  general 
the  territory  damaged  has  not  been  particularly  valuable  for  farming 
purposes.  Where  the  coal  lies  at  greater  depths,  gentle  sags  from 
1  to  3  feet  deep  may  occur. 

Little  litigation  in  this  district  has  resulted  from  subsidence.  It 
is  generally  recognized  that  the  mining  of  the  coal  at  shallow  depths 
must  cause  surface  damage,  and  the  coal  is  relatively  much  more 
valuable  than  the  surface  in  Jackson  County. 

District  III 

This  district  includes  room-and-pillar  mines  on  coals  No.  1  and 
No.  2  in  the  northwestern  part  of  the  State.  The  mines  of  this 
district  were  not  visited  in  connection  with  this  investigation,  but 
some  data  upon  subsidence  have  been  collected  in  connection  with 
other  investigations.  The  commercial  coal  beds  lie  at  shallow  depths, 
a  large  proportion  of  the  mines  being  opened  by  slopes  and  drifts.  In 
general  the  room-and-pillar  system  of  mining  is  employed. 

The  deepest  mine  examined  in  the  district  during  the  cooperative 
investigation  is  210  feet  deep,  but  the  most  of  the  hoisting  shafts 
are  not  over  100  feet  deep.  In  several  of  the  mines  where  under- 
ground conditions  are  favorable,  the  longwall  system  can  not  be  used 
because  the  lowering  of  the  surface  and  the  breaking  of  the  thin 
rock  cover  is  likely  to  permit  the  inflow  of  water  and  sand. 

In  parts  of  the  district  conditions  permit  of  systematic  pillar 
drawing  and,  where  a  large  percentage  of  the  pillar  coal  is  removed, 
surface  subsidence  occurs.  Owing  to  the  thick  surficial  beds,1  con- 
siderable draw  is  likely  to  result  from  extensive  falls.  In  several 
places  the  movement  of  surficial  material  has  extended  laterally  a 
considerable  distance,  and  in  one  case  reported  farm  buildings,  not 
undermined,  have  suffered  damage. 


JThe  log  of  one  of  the  shafts  records  125  feet  of  surficial  material. 


SUBSIDENCE   DATA  79 

Where  pillars  are  drawn  and  extensive  falls  occur,  cracks  2  to 
12  inches  wide  have  appeared  on  the  surface  within  a  period  of  two 
weeks  to  three  months.  The  depression  following  the  removal  of 
44  inches  of  coal  has  varied  from  12  to  20  inches,  the  average  being 
40  per  cent  of  the  thickness  of  the  coal.  Where  the  cover  is  thin  and 
the  surficial  beds  are  deep,  pit  holes  will  form  instead  of  sags.  Ow- 
ing to  the  hilly  nature  of  the  country  little  damage  has  resulted 
by  the  formation  of  sags. 

Comparatively  little  litigation  has  been  due  to  subsidence  in  this 
district,  most  of  the  claims  for  damages  having  been  adjusted  by  the 
interested  parties. 

District  IV 

This  district  includes  the  room-and-pillar  mines  on  coal  No.  5 
in  the  north-central  part  of  the  State.  The  surface  in  District  IV 
is  in  part  flat,  and  in  part  hilly.  The  important  coal  bed  outcrops 
in  the  northern  and  western  counties  and  reaches  a  depth  of  600 
feet  in  parts  of  Macon  County.  Coal  is  mined  extensively  at  a  number 
of  points ;  in  all  there  are  about  250  mines,  shipping  and  local,  in 
the  district.  The  average  thickness  of  the  coal  is  given  as  4  feet  8 
inches.2  In  most  of  the  mines  either  the  room-and-pillar  system 
or  a  modified  panel  system  is  used.  However,  in  several  mines  the 
longwall  system  is  employed. 

In  but  few  of  the  room-and-pillar  mines  are  the  pillars  drawn, 
and  the  average  extraction  for  the  room-and-pillar  mines  of  the  dis- 
trict is  54  per  cent.  In  one-half  the  mines  included  in  the  coopera- 
tive investigation,  squeezes  have  occurred.  "Where  there  have  been 
so  many  squeezes  under  comparatively  shallow  cover  surface, 
subsidence  is  to  be  expected.  Surface  cracks  and  subsidence  seem 
to  be  related  to  the  absence  of  limestone  cap  rock.  Where  sandstone 
is  the  cap  rock  subsidence  is  more  marked."3 

In  the  special  study  of  subsidence  in  this  district  15  mines  were 
visited,  and  in  all  some  subsidence  was  apparent  or  reported  by  the 
mining  company.4  In  but  few  places  has  serious  damage  resulted. 
Owing  to  the  incomplete  removal  of  the  coal  over  any  large  areas,  in 
most  of  the  room-and-pillar  mines  of  the  district  the  pillar  coal  pre- 
vents subsidence  in  the  form  of  extensive  and  regular  sags.     Where 


2Andros,  S.  O.,  Coal  mining  practice  in  District  IV  :  111.  Coal  Mining  Investigations 
Hull.    12,  p.   15,  1915. 

3Idem,   p.    29. 

4Tt  should  he  stated  that  it  was  the  general  plan  to  visit  mines  at  which  it  was  re- 
ported that  suhsidence  had  occurred.  The  15  mines  visited  were  more  or  less  typical  mines, 
hut   it  should  not  he   inferred  that  suhsidence  has  occurred  at  all  the  mines   of  the  district. 


80  SURFACE    SUBSIDENCE   IN    ILLINOIS 

subsidence  occurs  over  the  parts  of  mines  in  which  all  the  pillar  coal 
has  not  been  recovered,  the  surface  may  be  broken  by  pit  holes  or  caves 
or  may  be  thrown  into  irregular  hummocks  and  sags.  Where  the 
coal  is  worked  near  the  outcrop,  extensive  areas  are  badly  broken  by 
caves  (see  figures  15  and  17).  Where  the  surficial  material  is  wet,  it 
may  run  into  the  rooms  when  the  roof  breaks.  The  wet  material 
may  slip  and  run  until  the  sides  of  the  cave  are  on  an  angle  of  25  to  30 
degrees.  Where  possible  some  of  these  holes  have  been  filled  and  now 
show  on  the  surface  as  sags  because  of  the  settling  of  the  filled  ma- 
terial. 

Data  on  10  fairly  typical  mines  are  given  in  the  accompanying 
table.  Except  for  the  two  shallow  mines,  the  extraction  averages 
about  55  per  cent. 

Table  10. — Data  on  subsidence  in  District  IV 


Depth  of  shaft 

Thickness  of 
coal 

Evidences  of  subsidence 

Feet 

Inches 

35 

58 

Surface  cracks  and  breaks,  pit  holes. 

75 

60 

Surface  cracks  and  breaks,  pit  holes. 

160 

54 

Sags  18  inches  deep ;  some  cracks. 

175 

72 

Sags  24  to  36  inches. 

185 

54 

Surface  rolling ;  some  cracks  and  sags. 

200 

72 

Sags  18  to  36  inches. 

200 

69 

Sags  12  to  18  inches. 

240 

69 

Sags  12  to  18  inches. 

245 

72 

Sags  12  to  18  inches. 

250 

69 

Sags  12  inches. 

Comparatively  little  litigation  has  been  the  result  of  subsidence 
in  this  district  except  where  the  mines  are  located  adjacent  to  large 
towns.  A  number  of  the  mining  companies  operating  in  the  suburbs 
of  towns  which  have  grown  toward  the  mining  location  have  been 
obliged  to  pay  claims  for  damages  to  residences  (see  figure  44).  One 
of  the  large  companies  reports  that  claims  for  damages  have  been  so 
excessive  that  it  has  been  found  expedient  to  leave  over  40  per  cent  of 
the  coal  to  prevent  subsidence.  The  president  of  this  company  claims 
that  coal  in  this  vicinity  is  worth  $200  per  acre  to  a  developed  mine 
and  $100  per  acre  to  a  new  mine.  On  this  basis  the  coal  left  in  the 
ground  is  worth  from  $40  to  $80  per  acre  mined. 

In  the  river  bottoms  the  principal  damage  following  mining  has 
been  the  formation  of  sags  that  have  been  filled  with  flood  water  in 
the  spring.  A  number  of  these  cover  extensive  areas  made  unfit  for 
cultivation  except  in  years  of  light  rainfall. 


SUBSIDENCE  DATA  81 

When  the  coal  right  is  not  owned  by  the  mining  company,  and 
the  coal  is  mined  on  a  royalty  basis,  the  mining  company  does  not 
usually  assume  liability  for  damage  to  the  surface.  Moreover,  it  is 
to  the  financial  interest  of  the  owner  of  the  coal  to  have  the  extraction 
as  complete  as  possible.  Considerable  coal  is  mined  on  this  basis  in 
this  district,  and  therefore  relatively  little  friction  exists  between  the 
agricultural  and  the  mining  interests. 

District  V 

The  principal  mines  of  Saline  and  Gallatin  counties  are  opened 
upon  coal  No.  5.  There  are  21  shipping  and  12  local  mines  in  the 
district.  In  Saline  County  the  average  thickness  of  the  bed  is  5  feet  4 
inches,  and  the  depth  from  25  to  400  feet.5 

The  problem  of  surface  support,  as  well  as  that  of  the  complete 
removal  of  the  coal,  is  made  more  difficult  by  the  occurrence  of  horses 
and  faults.  Mining  is  conducted  by  the  room-and-pillar  system,  and 
the  percentage  of  coal  gained  in  the  mines  examined  in  the  cooperative 
investigation  ranged  from  58.6  to  81.5,  the  average  of  seven  mines 
being  67.1. 

In  the  mines  along  the  outcrop,  considerable  damage  results  to 
the  surface  by  breaks  and  pit  holes  (see  figure  13).  When  the  coal 
lies  at  greater  depths,  cracks  and  sags  may  occur  over  the  squeezes  and 
extensive  falls. 

In  figure  14  are  shown  two  areas,  A  and  B,  which  subsided  as  a 
result  of  squeezes  adjacent  to  dikes.  A  5-foot  coal  bed  is  mined  at 
an  approximate  depth  of  300  feet.  The  depressions  are  about  2  feet 
deep  and  are  flooded  part  of  the  year.6  In  another  mine  in  the  same 
district,  due  to  the  mining  of  a  6-foot  coal  at  a  depth  of  265  feet,  sub- 
sidence occurred  adjacent  to  a  fault.  The  break  on  the  surface  ap- 
peared 6  hours  after  the  mine  examiner  had  passed  through  the 
workings  below.    The  surface  subsided  2  feet  6  inches. 

Mr.  R.  Y.  Williams  reports  that  in  another  mine  in  the  same  dis- 
trict a  squeeze  occurred  December  23  to  26,  1914.  The  area  affected 
underground  covered  about  three  acres.  The  squeeze  occurred  on 
the  northeast  side  of  a  dike.  Figure  15  shows  the  mine  workings  in 
relation  to  the  dike.  A  number  of  pillars  had  been  drawn  where  the 
coal  was  about  8  feet  thick  and  where  the  cover  was  approximately 
150  feet.     The  logs  of  holes  No.  2  and  No.  3  are  given  below. 


BAndros,   S.    O.,   Coal   mining  practice  in   District  V :    111.    Coal   Mining  Investigations 
Bull.   6,  p.   9,   1914. 

flIt  is  estimated  that  tile  could  be  laid  for   M   mile  for  $400. 


82 


SURFACE    SUBSIDENCE    IN    ILLINOIS 


The  rooms  were  28  feet  wide,  and  the  pillars  12  feet.  In  order  to 
stop  the  squeeze,  cogs  6  to  8  feet  square  were  built  of  4-  to  6-inch 
timber  and  filled  with  gob.  Some  of  the  cogs  were  10  to  12  feet  long 
by  6  to  8  feet  wide.  On  the  surface  a  few  cracks  appeared,  but  as  the 
country  is  rolling  it  was  impossible  to  observe  the  movement  of  the 
surface  without  the  taking  of  measurements. 

Log  of  drill  hole  No.  2 
(Elevation  at  surface  341.24) 


Description   of   strata 


Thickness 


Depth 


Surface    

Sand  shale   

Fire  clay 

Sand   rock    

Blue   shale    

Coal    

Blue   shale    

White  sand  rock 

Blue   shale    

Black  slate   

Coal    

White  sand   rock 

Blue  shale    

Coal    

Sand    rock    


Ft. 

18 

20 

1 

10 
29 
2 
2 
3 
14 
4 

3 

42 

6 


in. 

Ft. 
18 
38 
39 
49 

in. 

1 

78 

1 

11 

81 

83 

86 

100 

9 

104 

9 

1 

104 

10 

3 

108 

1 

150 

1 

4 

156 

5 

10 

157 

3 

Log  of  drill  hole  No.  3 
(Elevation  at  surface  285.09) 


Description  of  strata 

1 
Thickness                               Depth 

Surface    

Ft. 

14 
6 
5 
5 
4 

15 
3 
3 

52 
9 

1 

n. 

Ft.                 1 
14 

20 

25 

30 

34 

49 

52 

55 
107 
116 

n. 

Sand  shale   

Sand   rock    

Blue   shale    

Black  slate   

Blue   shale    

Iron  bowlder  

Coal    

Gray  shale    

Coal    

0 

2 

SUBSIDENCE    DATA 


83 


Table  11. — Data  on  subsidence  at  typical  mines  in  District   V 


Depth  of 

shaft 

Thickness  of 
coal 

Evidences  of  subsidence 

Feet 

Inches 

150 

72 

Sag  24  inches  deep. 

225 

72 

Sag  30  inches  deep   (near  a  fault). 

300 

60 

Sag  24  inches  deep   (near  a  fault). 

400 

56 

Sag  18  inches  deep. 

Little  litigation  in  this  district  has  been  due  to  surface  subsidence. 
Owing  to  the  hilly  nature  of  the  surface,  the  sags  cause  practically  no 
damage  to  farm  lands. 


District  VI 

This  district  includes  the  mines  opened  on  coal  No.  6  east  of  the 
Duquoin  anticline.  There  are  78  shipping  mines  in  this  district  varying 
in  depth  from  shallow  mines  along  the  outcrop  to  shafts  a  little  over 
700  feet  deep.  The  average  thickness  of  the  coal  is  9  feet  5  inches, 
the  range  being  from  7J/2  to  14  feet.7    In  the  year  ended  June  30,  1914, 

folio    (No.    185),    1912. 

the  mines  of  the  district  produced  about  23.5  per  cent  of  the  tonnage 
of  the  entire  State.  In  1914  the  extraction  reported  by  the  operators 
was  56  per  cent  of  the  coal  in  the  bed.8 

Most  of  the  coal  is  free  from  horses,  rolls,  and  faults.  The 
nature  of  the  roof  and  floor,  as  well  as  of  the  overlying  strata,  has 
been  discussed  in  Chapter  II. 

Subsidence  has  occurred  at  many  mines,  both  at  those  along  the 
outcrop  and  at  some  of  the  deepest  mines  of  the  district.  "With 
present  dimensions  when  rooms  have  been  driven  200  to  300  feet 
there  is  a  large  area  of  unsupported  cap  rock.  If  an  attempt  is  made  to 
draw  pillars  under  such  conditions  a  squeeze  is  usually  started  which 
often  rides  over  room  and  entry  pillars  and  sometimes  affects  large 
acreage.    In  one  mine  a  squeeze  covered  85  acres ;  in  another  80."8 

Data  on  subsidence  were  secured  at  30  shipping  mines.  It  has 
been  impossible  to  formulate  any  definite  statement  in  regard  to  the 
average  amount  of  subsidence  that  has  occurred  or  that  may  be  ex- 
pected for  different  depths  and  when  specific  percentages  of  coal  are 
extracted.  The  statement  is  made  generally  throughout  the  district 
that  if  40  per  cent  of  the  coal  is  left  in  room  pillars  there  will  be  no 
surface  subsidence.     This  statement  should  undoubtedly  be  qualified, 


7Shaw,   R.  W.  and  Savage,  T.   E.,  U.   S.   Geol.   Survey  Geol.  Atlas,  Murphysboro-Herrin 
RAndros,   S.    ().,   Coal   mining  practice  in   District   VI:    111.    Coal   Mining   Investigations 


Bull.   8,  p.    15,    1914. 


84 


SURFACE    SUBSIDENCE   IN   ILLINOIS 


and  the  maximum  width  of  room  specified  for  various  depths  as  well 
as  the  percentage  of  coal  to  be  left  in  pillars. 

At  a  few  places  levels  have  been  run  on  the  surface  both  before 
and  after  subsidence.  When  the  mining  companies  have  reported 
subsidence  and  have  given  the  depth  of  a  depression  on  the  surface,  the 
depth  given  has  usually  been  an  estimate  or  a  measurement  of  the 
depth  of  the  deepest  part  of  the  sag  below  the  general  level  of  the 
surrounding  territory. 

The  most  reliable  of  the  data  collected  in  the  district  are  con- 
densed and  presented  in  Table  12. 


Table  12. — Data  on  subsidence  at  typical  mines  in  District  VI 


Thickness 

Depth  of  shaft 

of  coal 

Evidences  of  subsidence 

Feet 

Inches 

100 

100 

Breaks  and  pit  holes. 

115 

96 

Sags  60  inches  deep   and  pits. 

118 

72 

Sags  60  inches  deep. 

119 

90 

Pit  holes. 

120 

108 

Sags  48  to  60  inches  deep  and  pits. 

140 

90 

Sags  40  inches  deep  and  pits. 

140 

108 

Sags  60  inches  deep  and  pits. 

147 

108 

Sags  48  inches  deep  and  pits. 

150 

90 

Sags  48  inches  deep  and  pits. 

190 

90 

Sags  24  inches  deep. 

215 

84 

Sags  36  inches  deep. 

220 

84 

Sags  36  inches  deep. 

325 

108 

Sags  36  inches  deep. 

350 

96 

Sags  48  inches  deep. 

409 

96 

Sags  30  inches  deep. 

417 

108 

Sags  48  inches  deep. 

443 

96 

Sags  30  inches  deep. 

460 

96 

Sags  48  inches  deep. 

517 

96 

Sags  36  inches  deep. 

Little  effort  has  been  made  to  restore  the  surface  where  pit  holes 
have  been  formed  (see  figures  12  and  19).  This  is  due  probably  to  the 
much  smaller  valuation  of  this  land  for  agricultural  purposes  than 
the  land  in  the  northern  part  of  the  State,  where  it  is  not  uncommon 
to  fill  the  holes  and  to  restore  the  general  slope  of  the  surface.  As  the 
country  is  much  more  hilly  less  damage  results  from  sags  and  from 
the  formation  of  ponds  and  swamps  than  in  the  prairie  lands  of 
District  I. 

Considering  the  amount  of  subsidence,  there  has  been  compara- 
tively little  litigation.     Claims  for  damage  to  the  surface  are  generally 


SUBSIDENCE   DATA 


85 


adjusted  out  of  court.  It  must  be  expected  that  in  this  district  of 
thick  coal,  where  coal  mining  is  probably  the  leading  industry,  more 
or  less  injury  to  the  surface  must  be  endured  if  the  coal  resources  are 
to  be  properly  utilized.  Moreover,  below  the  coal  bed  now  being 
worked  are  other  beds  which  undoubtedly  will  attract  attention  after 
coal  No.  6  has  been  worked  out,  and  this  deeper  mining  may  also  be 
expected  to  cause  surface  movement  in  part  of  the  district. 

District  VII 


This  district  includes  all  mines  operating  in  coal  No.  6  west  of  the 
Duquoin  anticline,  and  north  as  far  as  an  east-west  line  about  6  miles 
south  of  Springfield.  The  150  shipping  and  46  local  mines  of  this 
district  produce  nearly  40  per  cent  of  the  entire  tonnage  of  the  State. 
The  thickness  of  the  coal  varies  from  2y2  to  14  feet,  the  average  being 
7  feet.  The  coal  outcrops  on  the  western  side  of  the  district  and  is 
deepest  in  Christian  County  where  one  shaft  has  opened  it  at  a  depth 
of  730  feet. 

The  coal  is  mined  by  the  room-and-pillar  and  panel  systems.  The  aver- 
age per  cent  of  recovery  is  55  ;  that  is  45  per  cent  of  the  coal  in  the  bed  is  left 
in  the  mine  and  probably  will  not  be  recovered  in  the  future.  Because  of  the 
large  area  of  this  district,  the  failure  to  bring  to  the  surface  a  proper  percentage 
of  the  coal  in  the  bed  is  a  matter  for  serious  consideration.  A  contributing 
cause  of  this  waste  of  natural  resources  is  the  fear  of  bringing  about  surface 
subsidence  and  attendant  damage  suits.     It  would  probably  be  economy  for  the 

Table  13. — Data  on  subsidence  at  typical  mines,  District  VII 


Depth  of  shaft 

Thickness  of 
coal 

Evidences  of  subsidence 

Feet 

Inches 

70 

72 

Sags  60  inches  deep  and  pit  holes. 

85 

72 

Pit  holes. 

160 

84 

Sags  40  to  50  inches  deep. 

190 

90 

Sags  48  inches  deep. 

300 

75 

Sags  24  inches  deep. 

325 

100 

Sags  12  to  60  inches  deep. 

328 

100 

Sags  42  inches  deep. 

330 

84 

Sags  30  inches  deep. 

385 

84 

Sags  20  inches  deep. 

400 

93 

Sags  24  inches  deep. 

408 

78 

Sags  30  inches  deep. 

430 

90 

Sags  14  inches  deep. 

435 

96 

Sags  18  inches  deep. 

450 

96 

Sags  14  inches  deep. 

466 

96 

Sags  12  to  18  inches  deep. 

470 

96 

Sags  18  inches  deep. 

585 

102 

Sags  24  inches  deep. 

86  SURFACE    SUBSIDENCE   IN    ILLINOIS 

operating  companies  to  purchase  the  surface  overlying  the  coal  to  be  removed. 
Pillars  could  then  be  robbed  and  30  per  cent  more  of  the  coal  bed  could  be 
recovered.9 

As  in  a  number  of  the  other  districts  few  data  are  available  to 
show  the  actual  difference  in  elevation  of  the  surface  before  and  after 
the  coal  has  been  removed.  In  most  of  the  observations  recorded  in 
Table  13  the  subsidence  has  been  estimated  or  measured  roughly  by 
comparing  the  elevation  of  the  low  point  of  a  sag  with  the  general 
slope  of  the  ground.  In  several  instances  the  depth  of  filling  required 
to  bring  railroad  tracks  to  grade  has  been  taken  as  an  indication  of  the 
amount  of  subsidence. 

In  several  of  the  smaller  mining  towns  considerable  damage  to 
residences  has  resulted  from  surface  subsidence,  and  some  litigation 
has  resulted,  but  most  claims  have  been  adjusted  out  of  court.  The 
mining  company  has  made  many  of  the  repairs  necessary  to  restore 
damaged  buildings.  One  mining  company  has  laid  draintile  to  remove 
water  standing  in  a  sag  caused  by  the  mining  of  coal,  and  thus  a  valu- 
able field  has  been  made  available  for  agriculture. 

District  VIII 

As  previously  noted  both  coals  No.  6  and  No.  7  are  mined  in  the 
Danville  district.  The  beds  lie  at  varying  depths,  the  deepest  shaft  in 
the  district  being  240  feet.  The  irregularities  in  the  coal  bed,  roof,  and 
floor  have  been  discussed  in  Chapter  II.  As  it  has  not  been  advisable 
to  drive  the  rooms  a  uniform  width  on  account  of  the  irregularities, 
pillars  have  been  gouged  in  a  number  of  mines.  The  percentage  of 
extraction  in  six  cooperative  mines  ranges  from  55  to  82  and  aver- 
ages 71.5. 

Adjacent  to  the  outcrop  where  the  coal  beds  have  been  mined  by 
the  room-and-pillar  system  large  areas  of  the  surface  have  been  dam- 
aged by  the  formation  of  pit  holes  (see  figures  16  and  35).  In  the 
deeper  mines  the  squeezes  that  have  frequently  resulted  from  gouging 
pillars  have  often  been  attended  with  surface  subsidence  (see  figures 
30  and  31).  The  land  back  from  the  streams  lies  flat  and  is  very 
fertile,  and  the  formation  of  sags  has  caused  considerable  litigation 
when  deed  to  the  coal  has  not  released  the  mining  company  from  lia- 
bility for  surface  damage.  Sags  have  been  measured  at  several  points, 
one  of  the  largest  measured  having  a  maximum  depth  of  4.7  feet. 
The  coal  bed  mined  in  this  vicinity  was  210  feet  deep  and  averaged  6 
feet  in  thickness. 


9Andros,  S.   O.,   Coal  mining  practice  in  District  VII:   111.   Coal  Mining  Investigations 
Bull.   4,  p.    16,    1914. 


SUBSIDENCE  DATA  87 

Some  damage  has  resulted  to  farm  buildings  and  dwellings,  largely 
because  the  coal  was  not  removed  completely  from  beneath  the  build- 
ings. A  building  standing  over  a  small  pillar  may  be  seriously  dam- 
aged by  the  draw,  and  if  the  pillar  left  is  not  directly  beneath  the  build- 
ing, the  building  will  be  cracked  seriously  or  broken  by  the  tilting  over 
the  shoulder  of  the  pillar  (see  figure  41). 


CHAPTER  V— PROTECTION  OF  SURFACE 
General  Considerations 

Though,  as  has  been  noted,  it  may  be  unwarranted  to  assume  that 
coal  may  be  removed  over  large  areas  without  disturbing  the  surface,  it 
is  well  known  that  over  small  areas  such  as  roadways,  rooms,  and  even 
small  panels  of  rooms,  the  coal  may  be  removed,  and  the  roof  will  arch 
or,  if  it  falls,  break  up  to  such  an  extent  that  the  broken  material  may 
fill  the  entire  volume  of  the  opening.  Under  such  conditions  severe 
subsidence  can  not  result.1 

Where  coal  beds  are  to  be  mined,  the  surface  above  may  be  pro- 
tected from  subsidence  in  several  ways.  In  general,  the  most  common 
and  the  most  feasible  are  (1)  by  the  use  of  pillars  or  artificial  supports 
and  (2)  by  filling  methods.2 

Pillars 

In  considering  the  service  which  a  pillar  may  render,  and  in  de- 
termining the  size  of  the  pillar  for  protecting  specific  mine  openings 
or  objects  on  the  surface,  it  will  be  necessary  to  consider  some  of  the 
following  factors,  in  some  cases  all  of  them: 

1.  Unit  strength  of  the  material  forming  the  pillar. 

2.  Height  of  the  mine  opening. 

3.  Dip  of  the  mineral  deposit. 

4.  Angle  of  "draw"  or  "drag"  or  "pull"  over  the  pillars  as  observed  in 

the  district  or  under  similar  conditions. 

5.  Angle  of  break  of  the  overlying  rock. 

6.  Strength  of  the  overlying  rocks. 

7.  Nature  and  amount  of  filling  in  the  mined-out  area  adjacent. 

8.  Depth  at  which  mining  may  be  carried  on  without  affecting  the  surface. 

9.  Bearing  power  of  the  bottom  or  floor. 

10.     Weight  of  overlying  materials  that  must  be  supported. 

Crushing  Strength  of  Coal 

Strength  tests  have  been  made  upon  Illinois  coal,  but  the  data 
secured  have  not  been  sufficient  to  warrant  the  formulation  of  rules 
based  upon  crushing  strength  alone.  Moreover,  the  advisability  of 
placing  much  reliance  upon  data  secured  from  such  tests  is  questioned 

^his  presumes  that  subsequently  the  weight  of  overlying  measures  does  not  compress 
the  broken  material  to  the  same  volume  it  occupied  when  solid. 

frequently  the  total  damage  to  the  surface  may  be  minimized  by  rapid  and  complete 
removal  of  the  coal. 

(88) 


PROTECTION    OF    SURFACE 


89 


by  many  mining  engineers  on  account  of  the  difficulty  of  securing  sam- 
ple blocks  of  coal  which  are  really  representative  of  the  entire  thick- 
ness of  the  coal  seam.  The  blocks  usually  tested  represent  the  strongest 
layer  of  coal,  the  weaker  bands  frequently  being  so  soft  that  a  repre- 
sentative sample  can  not  be  secured.  Where  the  weight  comes  on 
pillars  of  such  banded  coal,  the  softer  bands  are  crushed,  and  the 
harder  bands  must  give  way  until  a  more  or  less  uniform  bed  of 
crushed  coal  furnishes  a  support. 

The  results  of  the  tests  upon  Illinois  coal  are  as  follows : 

Table  14. — Compression  tests*  of  Illinois  coals 


6 

Equivalent 

Location 

section 

Height 

Maximum   load 

Top       Bottom 

Inches 

Inches 

Inches 

Lbs. 

Lbs. 
per  sq.  in. 

12,401 

Penwell  Coal  Co.,  Pana. . . . 

111x12 

111x12 

124 

316,000 

2,090 

12,402 

Empire  Coal  Co 

i5ixl7§ 

15  xl5i 

11.3      540,000 

2,170 

12,403 

W.  W.  Williams,  Litchfield. 

13ixl3I 

14  xl4 

141       186,000 

1,000 

12,404 

Herdien  Coal  Co.,  Galva... 

1Ux17:1 

16  xl3 

12         208,000 

1,020 

12,405 

T.  H.  Watson,  Litchfield.  . . 

131x12 

131x12 

15         224,000 

1,360 

12,406 

C,  W.  &  V.  Coal  Co., 

Streator 

tlfx  9] 

11   xlli 

13 

140,000 

1,280 

*Talbot,  A.   N.,  Compression  tests  of  Illinois  coals:   111.   State  Geological  Survey  Bull. 
4,   p.    199,    1907. 


Angle  of  Break  and  Angle  of  Draw 

Considerable  discussion  has  been  carried  on  in  Illinois  in  regard 
to  the  angle  of  break  and  the  angle  of  draw.  European  engineers  who 
have  studied  subsidence  for  a  number  of  years  have  observed  that  there 
is  a  first  break  and  then  a  main  or  after-break.  The  so-called  "first 
break"  corresponds  more  or  less  to  the  break  observed  in  the  immediate 
roof  as  the  longwall  face  advances. 

Mr.  S.  O.  Andros  in  discussing  mining  practice  and  conditions 
in  the  longwall  field  of  Illinois  states  that  subsequent  to  the  first  break 
at  the  shaft  pillar  and  face,  if  the  gob  area  has  been  properly  filled 
so  that  the  roof  weight  rides  on  the  face  of  the  coal,  other  roof  breaks 
occur  every  2  inches  to  6  feet  parallel  to  the  coal  face  extending  upward 
away  from  the  face  and  toward  the  gob  as  the  face  advances.  The 
distance  between  breaks  depends  principally  upon  the  character  of  the 
roof  and  the  packing  of  the  gob.  At  the  face  of  solid  coal  the  cracks 
in  the  roof  are  difficult  to  see ;  and  they  do  not  become  easily  visible 
(fig.   50)    until  the   face  has  advanced  4  to   5   feet.     The  distance  to 


90 


SURFACE    SUBSIDENCE    IN   ILLINOIS 


which  these  mining  breaks  extend  into  the  roof  depends  upon  the  roof 
material,  but  they  rarely  extend  more  than  15  feet  above  the  coal.  The 
angle  made  by  these  breaks  varies  from  50  to  90  degrees  from  the 
horizontal,  depending  upon  the  roof  material  and  the  rate  of  settling. 
In  summer  when  the  face  progresses  slowly  the  cracks  are  more  nearly 
vertical.3 

In  a  number  of  places  it  has  been  possible  to  observe  the  effect 
of  subsidence  upon  the  strata  10  to  20  feet  above  longwall  workings. 
As  reported  by  Mr.  Andros,  very  few  cracks  have  been  in  evidence  in 
the  overlying  shales  and  the  strata  have  apparently  settled  gradually 


Fig.  50.— Cracks  in  the  immediate  roof  of  a  longwall  mine  in  the  La  Salle 
area.     (Photo  by  S.  O.  Andros.) 


and  with  but  little  fracturing,  and  such  cracks  as  have  resulted  have 
evidently  closed  after  the  face  has  advanced. 

Though  the  observations  in  Illinois  supported  the  general  state- 
ment that  the  breaks  extend  back  over  the  gob  and  are  usually  not 
evident  at  a  height  of  more  than  20  feet  above  the  coal  bed,  practically 
no  available  data  support  or  oppose  the  theory  and  observations  of 
European  engineers — namely,  that  the  angle  of  break  in  the  immediate 


3Preliminary    report    on    organization    and    method : 
Bull.    1,  p.   20,    1913. 


111.     Coal    Mining    Investigations 


PROTECTION    OF    SURFACE 


91 


roof  is  practically  unimportant  and  that  the  important  angle  is  the 
angle  of  draw  (this  of  course  refers  to  stratified  rocks). 

In  discussing  these  angles  the  German  engineer,  Wachsmann,  illus- 
trated his  observations  by  figure  5.  The  beds  directly  over  the  worked- 
out  portion  of  the  coal  are  broken  by  subsidence  depending  largely  upon 
the  amount  and  the  nature  of  the  packing.  This  zone  of  breaking  is 
limited  by  the  plane  through  BE.  However  the  measures  beyond  BE 
are  disturbed  by  the  sinking  of  the  beds  immediately  over  the  mine 
workings  and  the  draw  may  extend  to  and  is  limited  by  the  plane 
through  CE.  It  is  then  the  angle  CED  which  is  important  rather  than 
the  angle  of  the  local  breaks  in  the  immediate  roof. 


Fig.  51. — Stress  diagram  of  an  ideal  homogeneous  cantilever  (after  Hal- 
baum). 

Similarly  British  engineers  have  noted  the  angle  of  the  local  breaks 
in  the  immediate  roof,  but  have  given  attention  to  the  angle  of  draw 
as  the  more  important  and  controlling  factor  in  determining  the  size 
of  shaft  pillars  and  in  indicating  the  probable  limits  of  the  general  sub- 
sidence over  extensive  mine  workings. 

Probably  this  phase  of  subsidence  has  been  discussed  in  more  detail 
in  a  paper  by  Mr.  H.  W.  G.  Halbaum  than  by  any  other  British  en- 
gineer. Owing  to  the  importance  of  a  correct  understanding  of  this 
phenomenon,  as  it  applies  to  longwall  mining  in  Illinois,  the  theory4  of 
Mr.  Halbaum  will  be  presented  in  some  detail. 

"It  may  be  conceived  that  the  measures  overlying  the  coal  bed  act 
as  a  cantilever  where  the  coal  is  undermined.    The  cantilever  rests  upon 


'Halbaum,   II.   W.   G.,  The  great  planes  of  strain  in  the  absolute  roof  of  mines:  Trans. 
Inst.    Min.    Engrs.    vol.    30,   p.    175,    1905-1906. 


92 


SURFACE    SUBSIDENCE    IN    ILLINOIS 


the  solid  unworked  coal,  the  load  consisting  primarily  of  the  weights 
of  the  measures  themselves.  The  cantilever  will  be  like  other  canti- 
levers in  certain  particulars.  It  possesses  a  neutral  surface.  Above 
this  surface  all  the  stresses  in  the  beam  of  strata  are  of  the  tensile 
order.  Below  it  all  are  of  the  compressive  order.  The  uppermost  ten- 
sile stress  and  the  lowermost  compressive  stress  are  the  maxima  of 
their  respective  orders;  and  both  orders  of  stress  regularly  diminish 


^^^mmm^^^^^^^^fi^^^^^^^^ 


Fig.  52.— Stress  diagram  of  a  low-down  neutral  surface  (after  Halbaum). 


as  the  planes  on  which  they  act  approach  nearer  to  the  neutral  surface, 
at  which  plane  both  kinds  of  stress  are  reduced  to  zero.  Figure  51 
shows  the  stress  diagram  of  an  ideal  homogeneous  cantilever,  whereas 
figure  52  shows  the  stress  diagram  of  a  cantilever  with  a  low-down 
neutral  surface.  In  figure  51  the  neutral  surface  is  at  NS,  at  half 
the  depth  of  the  beam.  The  stresses  in  the  upper  section,  a,  are  ten- 
sional,  and  the  stresses  in  the  lower  section,  b,  are  compressive.  ABC 
is  the  absolute  line,  and  AC  is  the  mean  line  of  elementary  strain ;  in 
this  case,  vertical.     In  figure  51  the  neutral  surface  lies  in  the  plane 


PROTECTION    OF    SURFACE  93 

NS.  AS  is  the  tensile  component;  SC  the  compressive  component;  and 
the  broken  line,  CA,  represents  the  mean  elementary  line  of  strain 
projecting  over  and  toward  the  solid." 

The  idea  that  the  main  angle  extends  toward  and  over  the  solid 
coal  is  generally  accepted  by  British  engineers.  According  to  this, 
subsidence  will  begin  before  the  coal  directly  below  (in  the  case  of 
horizontal  beds)  has  been  mined.  The  size  of  this  main  angle  is  vari- 
able and  depends  upon  the  nature  and  dip  of  the  strata  and  on  the 
amount  and  character  of  the  filling. 

In  Illinois  a  number  of  subsidences  have  been  reported  to  have 
occurred  in  advance  of  the  longwall  face.  Where  pillars  have  been  left 
to  protect  definite  areas  or  buildings,  it  has  been  found  that  there  is 
some  subsidence  over  the  edge  of  the  pillar,  but  it  is  generally  believed 
that  this  movement  will  occur  only  after  the  working  face  has  been 
stopped  for  some  time.  Few  data  are  available  in  Illinois  either  to 
prove  or  disprove  the  proposition  that  the  wave  of  subsidence  extends 
ahead  of  the  longwall  face  as  it  advances.  At  one  of  the  shallow  mines 
in  the  longwall  district  a  borehole  was  put  down  in  advance  of  the 
coal,  and  when  the  longwall  face  reached  the  borehole  an  examination 
of  the  surface  was  made.  It  was  found  that  subsidence  had  extended 
to  the  collar  of  the  borehole  and  did  not  lag  behind  the  longwall  face. 

Safe  Depth 
theory  as  previously  advanced 

It  has  been  argued  by  various  engineers  and  mine  managers  that 
there  is  a  depth  below  which  it  is  feasible  to  remove  all  the  coal  without 
disturbing  the  surface  and  without  introducing  filling  or  making  any 
special  provision  for  filling.  This  theory  is  founded  upon  the  assump- 
tion that  after  the  coal  has  been  mined  the  overlying  beds  break  and  fall 
and  fill  up  the  cavity  produced  by  the  removal  of  the  coal.  There  is 
little  evidence  available  in  Illinois  on  which  to  base  this  theory,  and  a 
number  of  American  engineers  who  have  studied  the  problem  agree 
that  the  "safe  depth"  theory  is  not  logical. 

INCREASE    IN    VOLUME    OF    ROCK    BY    BREAKING 

In  order  that  the  effect  of  caving  and  crushing  of  overlying  beds 
may  be  understood,  it  is  important  that  the  volume  occupied  by  broken 
material  be  compared  with  the  volume  occupied  by  a  unit  of  the  same 
material  when  unbroken  "in  the  solid."  Extensive  tests  have  been 
made  by  engineers  to  determine  to  what  extent  the  volume  of  rock 
may  be  increased  by  crushing  to  various  sizes.     The  French  engineer 


94 


SURFACE    SUBSIDENCE    IN    ILLINOIS 


Fayol  made  elaborate  tests,  the  results  of  which  are  shown  in  con- 
densed form  in  the  accompanying  table. 

Table    15. — Volumes   of  different    materials   after   crushing   as   compared   with 

volume  "in  the  solid" 


Nature  of  rock 


Relative  volumes 


1% 


™E 


>  £°  y 


.5  £^f, 
n!    ^  y 


.■S;§»a 

«   *°  y 


~-0  ^ 

K   g   » 

4)  rt  3 


2  C 


Clay  .... 
Shale  .... 
Sandstone 
Coal 


100 
100 
100 
100 


196 
213 
219 
207 


209 
210 
214 
224 


226 
221 
211 
199 


225 

-216 

224 

229 

310 

214 

223 

202 

COMPRESSIBILITY    OF    BROKEN    ROCK 

Experiments  have  been  made  upon  crushed  material  to  determine 
to  what  extent  it  may  be  compressed.  In  general  it  is  known  to  what 
extent  rock  in  place,  when  crushed  to  a  specified  size,  may  occupy  an 
increased  volume  when  the  crushed  material  is  subjected  to  pressure. 
Fayol's  results  of  compression  tests  upon  crushed  material  are  given 
in  Table  16. 


Table  16. — Compressibility  of  different  materials  after  having  been  crushed 


c 

Rocks  having  been   previously  crushed   or   broken   occupy 
space  indicated,  under  pressure* 

to 

o 
o 

Space  occu- 
pied before 
being  broke 

I 

Pressure 

1,422  1b. 
per  sq.  in. 

II 

Pressure 

2,844  lb. 
per  sq.  in. 

Ill 

Pressure 
7,110  1b. 
per  sq.  in. 

IV 

Pressure 
14,220  1b. 
per  sq.  in. 

Clay     

Shale     

Sandstone    .... 
Coal     

100 

100 
100 
100 

100                   90 
128                  116 
136                  125 
130                  125 

75 
110 
120 
118 

70 

97 

105 

109 

The  following  conclusion  was  drawn  by  Fayol :  "The  material 
which  ordinarily  fills  the  graves  of  mines  always  occupies  a  larger 
space  than  it  did  ordinarily.  After  an  expansion  of  about  60  per  cent, 
it  appears  to  undergo  in  workings  of  from  300  to  900  feet  in  depth,  a 
compression  of  about  30  per  cent,  which  leaves  a  volume  of  about  12 
per  cent  larger  than  the  volume  of  the  unbroken  rock."5 


*  Pressure   I  corresponds  to  a  depth   of  strata  of   1,638  feet;   II,   3,276  feet;    III,  8,190 
feet;   and   IV,   16,380  feet. 

BColliery   Engineer,  vol.   33,  p.   548,    1913. 


PROTECTION    OF    SURFACE  95 

The  United  States  Bureau  of  Mines0  had  made  tests  upon  crushed 
material  from  the  Pennsylvania  anthracite  districts  (Table  17)  to  de- 
termine its  compressibility  (1)  when  confined  in  steel  cylinders,  (2) 
when  built  into  cogs,  and  (3)  when  piled  in  heaps. 

Table    17 .—Compressibility   tests   upon   crushed   material  made    by    the    United 

States  Bureau  of  Mines 

Lbs-  Per  Corresponding  depth,  Compression 

SQ-    £t-  140  lbs.  per  cu.  ft.  (Reduction  in  height) 

Feet  Per  cent 

A.  Broken  mine  rock  and  breaker  refuse  compressed  in  a  steel  cylinder  16% 

inches  in  diameter  and  25^  inches  high  : 

20,000  143  11.4 

30,000  215  15.5 

90,000  645  24.0 

120,000  860  26.2 

B.  Mine    rock  passing   1^-inch   ring,   lying   loosely  in  a   conical   pile   and    free 

to  flow  : 

23,824  170  60.0 

40,256  290  62.3 

92,445  660  65.0 

165,000  1,180  67.0 

C.  Rock  cog,  built  of  mine  rock  and  shoveled  material.     Pyramidal  form;  base 

5  by  5  feet ;  top,  3  by  3  feet ;  height,  1  foot  1 1  inches. 

22,000                                          167  22.0 

30,000                                         215  27.0 

90,000                                        645  36.0 

120,000                                        860  37.2 

From  these  data  it  may  be  stated  that  for  the  conditions  of  long- 
wall  mining  where  the  gob  is  well  filled  and  the  walls  well  built,  the 
compression  of  the  gob  will  be  only  33 ]/$  per  cent  more  for  a  mine  645 
feet  deep  than  for  a  mine  215  feet  deep.  Data  are  not  available  to 
show  how  much  the  broken  shale,  commonly  forming  the  gob  in  the 
longwall  district,  will  be  compacted  under  pressure.  The  weight  of 
100  feet  of  overburden  is  sufficient  to  make  it  deform  and  flow. 

Where  the  mine  roof  falls  into  a  free  space  it  may  be  more  or 
less  shattered,  and  as  overlying  beds  fall  successively,  the  worked-out 
volume  may  be  filled  eventually.  The  material  which  can  not  fall  sinks 
upon  the  fallen  material  which  may  have  been  already  compressed  to 
such  an  extent  that  it  may  be  able  to  check  further  subsidence. 

In  longwall  mining  the  argument  has  been  that,  as  the  beds  over- 
lying the  gob  subside,  they  compress  the  gob  to  a  fraction  of  the  thick- 

"Unpublished  data. 


96  SURFACE    SUBSIDENCE   IN   ILLINOIS 

ness  of  the  coal,  and  that  as  they  sink  they  increase  in  volume  suffi- 
ciently to  prevent  the  movement  extending  to  any  great  height  above 
the  coal  horizon.  As  previously  noted,  observations  in  the  Longwall 
District  of  northern  Illinois  tend  to  prove  that  as  the  roof  along  the 
roadways  sinks,  it  breaks,  and  that  cracks  are  formed  extending  parallel 
to  the  working  face.  These  may  be  from  2  inches  to  6  feet  apart  and 
usually  extend  up  into  the  roof  shale  for  a  distance  not  exceeding 
15  to  20  feet.  Above  this  height  no  cracks  are  in  evidence  as  the  con- 
fined rock  flows  or  is  deformed. 

On  the  basis  of  these  observations  there  is  little  justification  for 
presumptions  or  theories  that  the  increase  in  volume  of  the  beds  sub- 
siding over  longwall  workings  is  sufficient  to  compensate  for  the  total 
height  of  material  mined.  Apparently  the  increase  in  volume  is  limited 
to  the  strata,  10  to  20  feet  thick,  immediately  overlying  the  coal  bed. 


Center  line  of  road 


Center  li 

O 


Fig.  53. — a,  Diagrammatic  illustration  through  the  gob  and  parallel  to  the 
face  of  a  longwall  mine ;  b,  plan  showing  pack  walls  and  loose  gob  between  road- 
ways and  cross  entries  in  the  same  mine. 

The  overlying  beds  are  traversed  by  breaks  or  cracks  "every  2  inches 
to  6  feet,"  and  it  is  evident  that  the  greatest  increase  in  volume  that 
can  arise  will  result  from  the  visible  breaks  or  cracks;  the  increase 
in  volume  resulting  from  invisible  cracks  may  probably  be  ignored 
without  serious  error.  If  the  visible  cracks  occur  every  2  inches  to  6 
feet,  the  material,  along  the  roads  at  least,  is  obviously  broken  into 
slabs  2  inches  to  6  feet  long,  and  these  slabs  settle  in  fairly  orderly 
fashion  upon  the  filling.  Under  such  conditions  any  considerable  in- 
crease in  volume  of  the  overlying  beds  is  not  conceivable.  If,  however, 
the  strata  higher  up  do  not  sink  gradually  but  remain  undisturbed  for 
a  time,  while  the  beds  immediately  underlying  subside  several  feet,  in 
time  such  resistant  beds  may  fail,  and  large  falls  may  occur  with  a 
considerable  increase  in  volume  of  the  broken  material.  In  northern 
Illinois  the  average  distance  between  room  centers  is  42  feet,  the  road- 


PROTECTION   OF    SURFACE  97 

ways  are  not  less  than  8  feet  wide,  and  the  pack  walls  are  4  yards  wide 
on  each  side  of  the  road.  The  distance  between  the  walls  should  there- 
fore average  about  10  feet.  This  space,  called  the  "gob,"  would  be 
filled  more  or  less  completely  with  waste  material  thrown  back  as  the 
face  is  advanced.  A  cross-section  along  the  face  would  then  show  the 
roof  supported  as  indicated  in  figure  53  a. 

There  is  little  probability  that  the  vertical  amount  of  settling  over 
the  gob,  if  not  more  than  10  feet  wide,  will  be  materially  greater  than 
the  settling  over  the  roads  which  are  8  to  10  feet  wide.  Moreover  an 
examination  of  old  roads  protected  by  pack  walls  or  buildings  shows 
that  as  the  roof  settles  the  pack  walls  are  compressed  and  they 
tend  to  bulge  and  to  spread  horizontally,  as  is  evidenced  by  the 
reduction  in  the  width  of  roadways.  It  may  logically  be  inferred  that 
some  spreading  of  the  pack  walls  occurs  on  the  side  toward  the  gob. 
In  time  the  gob  would  offer  more  resistance  to  settling  than  do  the 
roadways  although  these  are  probably  better  protected  at  first,  inasmuch 
as  the  pack  walls  are  built  more  substantially  on  the  roadside  than  on 
the  gob  side. 

Where  roads  have  been  driven  through  abandoned  longwall  work- 
ings in  which  the  old  roads  have  been  closed  for  years,  it  has  been 
found  on  brushing  to  the  necessary  height  for  the  new  road,  that  there 
is  but  little  undulation  in  the  previously  horizontal  roof  shales  on  ac- 
count of  the  settling  over  the  pack  walls.  If  such  undulation  exists  it 
is  undoubtedly  much  more  marked  in  the  strata  immediately  overlying 
the  coal  than  in  those  at  a  greater  height  above  the  coal  horizon.  From 
the  observations  that  have  been  made  in  the  deeper  longwall  mines  in 
Illinois,  where  the  measures  immediately  overlying  the  coal  are  thick 
beds  of  shale,  it  is  apparent  that  minor  irregularities  in  filling  and  pack 
walls  have  but  little  effect  upon  the  general  subsidence  movement; 
in  fact,  so  little  that  only  the  most  precise  observations  may  indicate 
that  such  irregularities  have  influenced  the  general  movement.  When 
it  is  so  impracticable,  as  is  usually  the  case,  to  secure  complete  data 
on  the  continuity  and  uniformity  of  the  overlying  beds,  it  seems  unwise 
to  attempt  to  discuss  the  effect  of  minor  irregularities  in  the  filling  and 
pack  walls. 

The  conditions  in  the  average  longwall  mine  may  be,  for  the  pur- 
pose of  discussion,  considered  to  be  as  shown  in  figure  53,/;.  As  the 
longwall  face  is  advanced  new  cross  entries  are  started  and  the  old 
ones  are  abandoned.  Where  the  cross  entries  are  turned  at  an  angle 
of  45  degrees  to  the  main  entry,  the  distance  between  cross  entries 
may  be  from  225  to  300  feet.7 


Preliminary    report    on    organization    and    method:     111.     Coal    Mining    Investigations 
Bull.   1,  p.    18,   1913. 


98 


SURFACE   SUBSIDENCE  IN   ILLINOIS 


From  these  cross  entries  are  turned  the  roadways  to  the  rooms 
or  working  places.  These  working  places  will  average  42  feet  in 
length  along  the  working  face,  and  the  distance  from  center  to  center 
of  roadway  will  be  42  feet.  As  shown  in  figure  53,  the  worked-out 
area  is  laid  out  more  or  less  regularly  in  a  series  of  parallelograms 
approximately  225  by  32  to  34  feet.  Around  the  four  sides  of  each 
parallelogram  is  a  wall  of  mine  rock  built  9  to  12  feet  thick.  Within 
the  four  walls  the  space  is  at  first  partly  filled  with  shoveled  material, 


A[ 


Cross  entry 


Cut  for  fire  wall 


JB 


Main   entry 


Plan 
Fig.  54.— Diagrammatic  illustration  showing  the  flow  of  roof  shale  under 
pressure  in  a  mine  near  Peoria. 

and  later  the  unfilled  space,  if  any,  may  be  filled  by  falls  of  roof  rock. 
After  the  working  face  has  been  advanced  a  short  distance,  the  roof 
settles  upon  the  pack  walls,  and  in  time  as  these  are  pushed  down  into 
the  underclay  the  roof  within  the  pack  walls  may  sag  and  bear  upon 
the  gob  (fig.  54).  When  this  state  is  reached,  the  parallelogram 
bounded  by  four  pack  walls,  becomes  in  reality  a  long  cog  with  walls 
built  of  mine  rock,  the  center  being  filled  with  shoveled  material. 


PROTECTION   OF    SURFACE  99 

These  cogs  tend  to  prevent  surface  subsidence.  Their  success  in 
accomplishing  this  will  depend  upon  the  extent  to  which  the  clay  bottom 
heaves  in  the  roads,  the  amount  the  pack  walls  bulge,  and  the  power 
of  the  pack  walls  and  the  gob  to  resist  compression.  As  usually  built 
these  walls  are  not  rigid. 

Normally,  when  the  main  entries  have  been  advanced  225  to  300 
feet  beyond  a  cross  entry,  a  new  cross  entry  is  started,  and  in  time 
the  old  cross  entries  are  abandoned.  Until  they  are  abandoned  suffi- 
cient height  is  maintained  to  permit  the  passage  of  mules.  The  roads 
are  brushed  and  the  bottom  is  lifted  as  long  as  it  is  necessary  to  keep 
the  road  open.  Though  the  amount  of  material  thus  removed  is  occa- 
sionally large,  relatively  it  represents  but  a  small  volume  of  the  material 
within  the  parallelograms  of  rock  filling  on  each  side  of  the  road. 
The  bulging  of  the  packs  and  the  flow  of  the  bottom  may  eventually 
cease  where  the  material  within  the  cog  has  been  compressed  to  such 
an  extent  that  it  does  not  flow  easily.  After  the  roads  have  been  aban- 
doned, the  amount  of  flow  is  limited  to  the  volume  of  the  roadway 
itself. 

For  the  purpose  of  this  discussion  it  may  be  assumed  that  two 
longwall  mines  are  operated  under  identical  conditions  except  that  the 
coal  seam  in  one  lies  at  a  depth  of  200  feet  and  the  other  at  600  feet. 
The  plan  of  mining,  dimensions  of  rooms,  and  other  factors  are  the 
same,  and  the  same  amount  of  material  is  built  into  walls  and  stowed 
in  the  gob. 

Considering  only  the  matter  of  compressibility  of  pack  walls  and 
gob,  it  should  be  noted  that  the  maximum  amount  of  subsidence  which 
can  result  in  the  mine  200  feet  deep,  is  determined  by  the  amount  the 
gob  and  walls  are  compressed  under  the  load  of  200  feet  of  overlying 
strata.  If  the  load  were  less,  the  distance  through  which  the  roof 
would  sink  would  be  less ;  and  if  the  load  were  increased,  the  distance 
through  which  the  roof  would  sink  would  be  increased  up  to  the  limit 
of  compressibility  of  the  material  in  the  gob. 

As  the  weight  of  the  overburden  increases  directly  with  the  depth, 
therefore  the  compression  of  the  gob  is  greater  for  deep  mines  than 
for  shallow  mines ;  it  is  greater  for  a  mine  600  feet  deep  than  for  a 
mine  200  feet  deep,  other  conditions  being  the  same,  providing  of  course 
that  the  limit  of  compressibility  of  the  material  has  not  been  reached. 
It  follows  logically  that  so  far  as  the  factor  of  compressibility  of  filling 
controls — and  in  a  majority  of  cases  it  is  the  controlling  factor — the 
total  amount  of  vertical  movement  tends  to  increase  rather  than  to  de- 
crease with  the  depth  of  mining. 

To  this  general  statement  there  may  be  exceptions,  and  there  may 
be  depths  beyond  which  this  would  not  apply;  but  it  is  the  opinion  and 


100 


SURFACE    SUBSIDENCE   IN    ILLINOIS 


the  experience  of  British  mining  engineers  that  subsidence  will  follow 
longwall  mining  irrespective  of  depth.  It  is  generally  supposed  that 
there  is  more  or  less  flow  in  the  rock  beds  overlying  the  coal  after  these 
beds  have  stood  for  a  time  depending  for  support  upon  the  pillars  or 
filling.  However,  it  is  difficult  to  find  evidences  of  such  flowage  on  a 
large  scale. 

In  a  mine  near  Peoria  it  became  necessary  to  open  a  section  of 
the  mine  that  had  been  abandoned  and  build  a  fire  wall  extending  up 
to  an  overlying  limestone.  Immediately  overlying  the  5-foot  coal  bed 
is  a  bed  of  shale  approximately  10  feet  thick,  and  resting  on  the  shale 
is  a  stratum  of  limestone.    The  roadway  from  12  to  15  feet  wide,  was 


Scale  of  Feet 
o  joo  eoo 

a  i  i— 


Fig.  55.— Diagrammatic  illustration  showing  to  scale  the  size  of  shaft  pil- 
lars for  given  depths  as  recommended  by  various  mining  engineers. 

filled  tightly  with  shale  from  the  overlying  bed.  A  cut  through  the 
shale  to  the  limestone  showed  that  the  shale  had  under  pressure  prac- 
tically flowed  to  fill  the  opening,  whereas  the  overlying  limestone 
showed  no  breaks  or  cracks  where  it  was  possible  to  make  an  examina- 
tion.    The  conditions  are  illustrated  by  figure  54. 


Shaft  Pillars 

Commonly  in  determining  the  size  of  pillars  necessary  to  protect 
mine  openings  of  a  given  width  it  is  customary  to  assume  a  span  of  roof 
and  overlying  rock  to  be  supported,  to  estimate  the  total  weight  of  such 


PROTECTION   OF    SURFACE  101 

a  block  for  the  depth  of  the  workings,  and  then  with  the  known  or 
assumed  unit  crushing  strength  of  the  material  to  be  left  in  the  pillar, 
the  cross-section  may  be  calculated  readily.  The  dimensions  may  then 
be  proportioned  in  order  to  secure  the  most  economical  and  safest 
working  conditions ;  on  the  same  general  plan  shaft  pillars  or  other 
important  pillars  may  be  determined. 

Numerous  rules  have  been  formulated  for  the  calculation  of  shaft 
pillars  in  flat  seams ;  a  great  diversity  of  opinion  prevails  among  en- 
gineers as  to  the  required  dimensions  at  various  depths  and  with  dif- 
ferent thicknesses  of  coal  seams.  This  diversity  of  opinion  is  well 
shown8  graphically  by  figure  55. 

In  determining  the  size  of  pillar  necessary  to  protect  objects  upon 
the  surface,  as  has  been  noted  previously,  the  ability  of  the  pillar  to 
carry  the  load  is  not  the  only  uestion  to  be  considered.  Among  the  most 
important  of  the  other  problems  is  that  of  draw  or  pull  over  the  pillar 
and  the  ability  of  the  underlying  bed  to  sustain  the  load  concentrated 
upon  it  by  the  pillar.  Quite  frequently  the  underlying  bed  is  less  stable 
and  has  less  crushing  strength  than  the  pillar.  It  seems  logical  then  to 
proceed  as  follows  in  determining  the  size  of  pillar  necessary  to  protect 
an  object  upon  the  surface: 

1.  Determine  the  lateral  extent  of  pillar  necessary  in  order  to  prevent  dam- 

age by  draw. 

2.  Determine    whether    the    pillar    thus    outlined    is    sufficiently    large    to 

support  the  burden  of  the  overlying  beds  without  crushing. 

3.  Determine   whether   the   load   upon   the  pillar  will   cause   the   pillar  to 

be  forced  down  into  the  underlying  bed,  or  cause  a  flow  of  the  under- 
lying material. 

Room  Pillars 

At  various  points  in  Illinois  it  has  been  necessary  for  the  coal 
mining  companies  to  assume  responsibility  for  any  surface  damage 
which  may  result  from  coal  mining  and  it  has  been  deemed  advisable 
to  leave  in  the  ground  a  sufficient  amount  of  the  coal  to  prevent  move- 
ment, at  least  to  prevent  the  movement  from  extending  to  the  surface. 

Where  the  roof  is  strong  it  may  stand  for  some  time  without 
breaking,  but  eventually  in  parts  of  the  mine  at  least,  movements  of 
the  top  or  bottom  may  cause  a  considerable  area  to  be  affected.  The 
general  theory  of  the  arching  of  strata  has  been  presented  by  a  French 
engineer,  Fayol. 


8Knox,    G.,    Mining    subsidence:     Proc.     International    Geological    Congress,    vol.     12, 
p.   798,    1913. 


102  SURFACE    SUBSIDENCE   IN    ILLINOIS 

In  his  discussion  of  methods  of  protecting  the  surface,  Fayol  re- 
ferred to  the  use  of  pillars  between  the  working  places.  "The  meshes 
of  the  network  consisting  of  pillars  with  working  places  between  them 
should  be  made  smaller  as  the  workings  are  shallower.  As  the  depth 
becomes  greater  the  size  of  the  meshes  can  be  enlarged,  and  the  dimen- 
sions of  the  areas  worked  can  be  increased  relatively  to  the  sizes  of  the 
pillars  that  are  abandoned,  regard  being  had  to  the  height  and  width 
of  the  zones  of  subsidence,  so  that  the  various  zones  may  be  kept  dis- 
tinct from  each  other.  This  general  rule  is  susceptible  of  many  com- 
binations according  to  the  thickness,  the  inclination,  the  number,  and 
the  depth  of  the  seams  worked.  If  the  excavation  is  of  small  dimen- 
sions the  subsidences  which  take  place  above  them  are  restricted  in 
size  and  become  enlarged  both  in  width  and  height  as  the  excavation 
increases  in  area.  If  the  pillars  at  1,  3,  5,  and  7  be  taken  out  (fig.  56), 
zones  of  subsidence  similar  in  Zx,  Z3,  Z5,  and  Z7  would  be  produced ;  but 
when  pillar  2  is  taken  out  the  line  of  roof  subsides  on  to  the  floor,  and 
the  zone  of  subsidence  rises  in  Z2.     The  same  thing  happens  when 


&*~M?''m.  zZk\  Vsr^rferSfer 


t-\ ; — r — r-<  — •)  ^~N\ 

J. i» 1 i L 


12       3      4-5      6,        7     8      3     JO      II     /Z    f3    14      J5 

Fig.  56.— Diagrammatic  illustration  showing  the  extent  of  subsidence  result- 
ing from  the  removal  of  adjacent  pillars  (after  Fayol). 

No.  6  pillar  is  taken  out,  and  if  No.  4  pillar  is  taken  out,  the  space 
comprised  between  the  zones  Z2  and  Z6  is  set  in  motion  and  deter- 
mines the  formation  of  the  zone  Z4."9 

It  follows  then  from  this  statement  of  Fayol,  that  if  the  room 
pillars  are  properly  proportioned  and  properly  spaced,  the  disturbance 
of  the  strata  may  be  limited  to  the  volume  within  the  zones.  The 
material  outside  these  zones  throws  no  weight  upon  the  material  within 
the  zone.  Necessarily  then  any  vertical  pressure  must  fall  upon  the 
unmined  material  forming  the  pillars,  and  the  pillars  must  be  large 
enough  to  withstand  this  pressure.  In  stratified  beds  the  problem  is 
more  complicated,  owing  to  the  fact  that  the  beds  act  as  single  members 
and  frequently  sag  under  their  own  weight. 


9Proc.  South  Wales  Inst.  Eng,  vol.  20,  p.  340,  1897.  It  should  be  noted  that  these 
zones  outline  the  dome  through  which  the  movement  extends,  and  not  the  limit  of  the 
"falling  zone"   as  described  by   the   Austrian   engineer,   Rziha. 


PROTECTION   OF    SURFACE 


103 


In  a  paper  before  the  Pennsylvania  State  Anthracite  Mine  Cave 
Commission,  1913,  Mr.  Douglas  Bunting  said,  "The  application  of  a 
formula  for  determining  the  safe  size  of  coal  pillars  for  various  thick- 
nesses of  veins  and  depths  can  be  considered  practical  for  depths 
greater  than  500  feet,  but  it  is  doubtful  if  the  same  formula  would  be 
of  any  practical  value  for  application  to  veins  at  less  depth,  and  cer- 
tainly of  diminishing  practical  value  with  reduction  in  depth  and  thick- 
ness of  veins  for  the  reasons  that  the  variable  conditions  of  vein,  top, 
bottom,  and  other  factors  are  of  more  consequence  with  small  pillars 
than  with  large  pillars."10  The  average  dimensions  of  pillars  and 
rooms  in  ordinary  room-and-pillar  mining  in  Illinois  are  shown11  in 
Table  16. 

Table  16. — Dimensions  of  rooms  and  pillars  in  Illinois  coal  mines 


District 


Average 
depth 


Room    width 


Pillar  width 


Feet 

Feet 

Feet 

II 

140 

26 

19 

Ill 

90 

22 

18 

IV 

201 

25 

9 

V 

243 

26 

16 

VI 

270 

22 

18 

VII 

227 

31 

30 

VIII 

174 

27 

8 

Average  for  State 

208 

26 

19 

Filling  Methods 


In  a  number  of  important  mining  districts  in  America  and  in 
Europe,  filling  methods  have  been  used  extensively  both  to  increase 
the  percentage  of  coal  recovery  and  to  reduce  the  surface  movement. 
These  methods  are  adapted  particularly  to  dipping  seams. 


GOBBING 

Waste  material  resulting  from  regular  mining  operations  or  broken 
for  this  particular  purpose  may  be  stowed  or  packed  into  the  excava- 
tion. If  sufficient  or  suitable  material  is  not  available  underground, 
it  may  be  lowered  or  dropped  from  the  surface  and  stowed  where 
needed. 


10Bunting,  D.,  Pillar  and  artificial  support  in  coal  mining  with  particular  reference  to 
adequate  surface  protection:  Pennsylvania  Legislative  Journal,  vol.  5,  Appendix,  p.  5988,  1913. 

11Andros,  S.  O.,  Coal  mining  in  Illinois:  111.  Coal  Mining  Investigations  Bull.  13, 
p.    76,    1915. 


104  SURFACE    SUBSIDENCE    IN    ILLINOIS 

In  the  longwall  field  the  waste  produced  at  the  working  face  is 
stowed  in  the  gob,  but  usually  a  large  amount  of  rock  resulting  from 
falls  and  brushing  in  the  roads  is  hoisted  and  piled  on  the  surface. 
Owing  to  the  nature  of  longwall  work  it  is  claimed  that  it  is  imprac- 
ticable to  stow  much  of  this  material  in  the  gob.  It  might  be  done  at 
an  increased  total  cost  per  ton  of  coal  mined. 

In  room-and-pillar  mining  the  waste  material  can  be  stored  under- 
ground much  more  readily  than  in  longwall  mining,  and  in  many  Illi- 
nois room-and-pillar  mines  practically  no  rock  is  hoisted. 

The  coal  beds  over  the  greater  part  of  Illinois  lie  practically  flat 
and  the  stowing  of  material  in  both  room-and-pillar  and  longwall 
mining  would  be  expensive  on  account  of  the  necessity  for  hauling 
the  filling  long  distances  and  because  a  large  amount  of  shoveling 
would  be  required  underground. 

HYDRAULIC    FILLING 

The  stowing  of  material  by  means  of  water12  has  been  employed 
extensively  in  a  number  of  mining  districts,  but  is  not  being  employed 
at  any  Illinois  coal  mines.  Hydraulic  filling  seems  to  be  impracticable 
at  present  on  account  of  the  flatness  of  the  beds,  the  clay  floor,  and 
the  difficulty  in  securing  suitable  filling  material  in  the  coal  district. 
As  previously  noted,  little  stone,  sand,  or  gravel  is  available,  and  the 
surface  is  so  valuable  for  agricultural  purposes  that  the  cost  of  material 
secured  from  surface  pits  would  be  prohibitive  in  most  places.  Deep 
pits  would  be  impracticable  generally,  as  considerable  pumping  would 
be  necessary  during  a  number  of  months  in  order  to  keep  the  pits 
unwatered.  In  parts  of  the  State  there  might  be  a  shortage  of  water 
during  several  months  of  the  year. 

Griffith's  method  of  filling 

It  has  been  suggested  by  Mr.  William  Griffith  that  worked-out 
portions  of  mines  be  filled  by  blasting  up  the  bottom  and  shooting  down 
the  roof.    This  suggestion  was  made  in  connection  with  a  report  to  the 


12The  Copper  Range  Consolidated  Copper  Company,  Painesdale,  Michigan,  is  using 
compressed  air  to  carry  filling  material  for  short  distances  through  iron  pipe.  The  material 
is  the  J4 -inch  "stamp-sand"  or  crushed  waste  rock  from  the  concentrating  plants  which  is 
dropped  from  the  surface  through  steeply  inclined  raises  to  the  levels  where  filling  is  being 
carried  on.  On  these  levels  the  material  is  dropped  into  cars  and  hauled  to  some  convenient 
point  above  the  stope  to  be  filled.  The  filling  material  is  dumped  from  the  cars  into  pockets 
or  chutes  and  is  distributed  horizontally  in  the  stopes  from  the  bottom  of  these  chutes.  It 
has  been  found  economical  to  carry  the  filling  material  by  compressed  air  not  to  exceed  300 
feet  through  the  pipes.  The  pipe  is  shifted  laterally,  lengthened,  shortened,  or  raised  as 
may  be  necessary  to  distribute  the  material.  There  are  no  bends  in  the  pipe  and  the 
material  is  handled  dry. 


PROTECTION    OF    SURFACE  105 

Scranton  Mine  Cave  Commission,  and  Mr.  Griffith  has  secured  a  patent 
(U.  S.  Patent  No.  1,004,418)  covering  this  method.13 

It  has  been  suggested  that  by  this  method  an  increased  percentage 
of  coal  could  be  recovered.  So  far  as  known  this  method  has  never 
been  applied  to  beds  as  flat  as  those  in  Illinois.  The  conditions  in  Illi- 
nois do  not  lend  themselves  toward  making  this  scheme  practicable  as 
the  immediate  roof  is  generally  not  hard  enough  to  make  the  proper 
kind  of  filling  and  the  bottom  is  underclay  which  is  too  soft  to  serve 
as  filling  that  will  increase  in  volume  when  blasted  and  in  that  condi- 
tion support  any  weight  without  being  reconsolidated  to  occupy  prac- 
tically the  original  volume. 

Artificial  Supports 

At  only  a  few  places  have  artificial  supports  been  introduced  to 
protect  objects  upon  the  surface.  The  construction  of  cogs  was  neces- 
sary at  one  place  to  prevent  the  collapse  of  the  beds  under  a  railroad 
right-of-way.  The  workings  were  at  shallow  depth  and  complete  filling 
seemed  to  be  impracticable  though  the  workings  were  still  accessible. 
Two  types  of  cogs  were  used,  the  more  successful  being  a  timber  cog 
filled  with  mine  rock.  Masonry,  concrete,  reinforced  concrete,  iron, 
and  steel  structures  have  been  employed  in  American  and  European 
districts  to  protect  important  structures  and  roads. 


13Messrs.  Griffith  and  Connor  say,  "It  is  a  well-known  fact  that  loose  rock  occupies 
from  If  to  twice  the  volume  of  the  same  weight  of  rock  in  place.  Your  engineers  have 
conceived  the  idea  of  taking  advantage  of  this  fact,  well  known  to  engineers,  for  the  purpose 
of  cheaply  producing  an  adequate  support  of  the  rock  and  surface  above  certain  classes  of 
coal  beds  under  the  city  of  Scranton.  So  far  as  we  know,  this  method,  in  its  entirety,  has 
never  been  used  before  in  any  coal-mining  district,  and  the  suggestion  is  here  made  for 
the    first   time. 

"The  process  is  applicable  to  beds  less  than  6  feet  in  thickness  and  consists  simply 
in  blowing  up  the  floor  and  shooting  down  the  roof  of  the  mine,  each  to  a  depth  equal  to 
the  thickness  of  the  coal  bed.  This  produces  a  total  thickness  of  loose  rock  equal  to  three 
times  the  thickness  of  the  coal.  The  rock  would  be  well  packed  together  and  have  great 
supporting  power,  and  moreover  the  desired  ends  would  be  attained  in  a  comparatively  in- 
expensive manner."— Griffith,  William,  and  Conner,  E.  T.,  Mining  conditions  under  the  city 
of  Scranton:   U.   S.   Bureau  of  Mines   Bull.   25,  p.   57,   1912. 


CHAPTER  VI— INVESTIGATIONS  OF  SUBSIDENCE 

European 

As  previously  noted  a  number  of  investigations  have  been  made  in 
Europe  to  determine  the  amount  of  subsidence  which  results  from  min- 
ing at  various  depths  and  under  different  geological  and  mining  condi- 
tions. Some  of  these  investigations  have  continued  over  long  periods 
of  years,  and  a  few  of  them  have  been  organized  so  that  additional 
data  will  be  secured  from  year  to  year.  It  has  been  possible,  in  districts 
where  such  observations  have  been  made,  to  adapt  the  system  of  mining 
so  that  the  maximum  recovery  of  mineral  may  be  made  with  least  dam- 
age to  the  surface.  Knowing  what  effect  mining  will  have  upon  the 
surface,  it  has  been  possible  for  several  countries  to  formulate  laws 
and  rules  for  the  protection  of  the  owner  of  the  surface  and  at  the 
same  time  to  secure  for  the  mine  owner  a  just  consideration  of  his 
rights.  The  problem  of  subsidence  in  Europe  has  been  discussed  by 
the  author  and  Mr.  H.  H.  Stoek  in  Bulletin  91  of  the  Engineering  Ex- 
periment Station,  University  of  Illinois. 

United  States 

In  the  United  States  very  little  work  has  been  done  along  these 
lines — practically  nothing  in  the  bituminous  coal  districts.  Very  few 
of  the  data  that  have  been  collected  are  available  for  the  use  of  the 
public.  The  scarcity  of  data  in  the  bituminous  fields  may  be  due  largely 
to  the  fact  that  the  most  extensive  mining  operations  for  bituminous 
coal  have  been  carried  on  where  the  surface  is  mountainous  or  is  of 
little  value  for  agricultural  purposes. 

If  the  percentage  of  extraction  from  the  flat  coal  beds  of  the 
Middle  West  is  to  be  increased  it  seems  timely  that  there  should  be 
secured,  in  more  or  less  typical  mining  areas,  data  which  will  serve 
to  show  the  amount  and  extent  of  subsidence  which  may  be  expected 
to  result  from  mining  operations. 

Suggested  Illinois  Investigation 
considerations 
It  has  been  suggested  that  in  Illinois  investigations  be  made  in- 
cluding measurements  to  determine  the  surface  movement  under  va- 
rious conditions  and  also  laboratory  tests  to  determine  the  strength 
of  rocks  forming  mine  roofs  and  of  materials  used  for  supports.  The 
bearing  power  of  the  materials  forming  the  mine  floor  should  also  be 
investigated.  The  nature  and  amount  of  surface  subsidence  should 
be  studied  when  different  methods  of  mining  are  used  and  when  various 
methods  of  filling  are  employed. 

(106) 


INVESTIGATIONS    OF   SUBSIDENCE  107 

TYPICAL    MINES 

The  idea  has  been  advanced  by  George  S.  Rice,1  that  typical  dis- 
tricts should  be  selected  giving  special  consideration  to  the  longwall 
fields.    For  this  work  the  following  may  be  suggested : 

1.  Wilmington  district  where  the  coal  occurs  at  a  depth  of  50  to  150  feet. 

2.  La  Salle  district  where  the  depth  to  coal  No.  2  is  from  300  to  500  feet. 

3.  Decatur  district  where  coal  No.  5  lies  at  a  depth  of  500  to  600  feet. 

4.  Assumption  district  where  coal  is  mined  at  a  depth  of  1,000  feet. 

For  the  investigations  in  connection  with  room-and-pillar  and 
panel  work  the  following  may  be  suitable : 

1.  Springfield  district  where  the  coal  is  mined  at  a  depth  of  150  to  200  feet. 

2.  Williamson  County  district  where  mining  is  at  varying  depths  up  to  300 

feet. 

3.  Gillespie-Staunton  district  with  depths  of  300  to  400  feet. 

4.  Franklin  County  district  where  the  depth  of  mining  is  400  to  700  feet. 

MONUMENTS    AND    SURVEYS 

It  has  been  suggested  that  substantial  surface  monuments  be  es- 
tablished in  parallel  lines  across  the  working  face  in  longwall  mines  and 
in  room-and-pillar  mines  across  panels  that  are  to  be  worked.  The 
monuments  should  be  established  over  the  solid  coal  before  any  move- 
ment has  commenced,  and  the  location  of  these  monuments  with  regard 
to  points  underground  should  be  determined  accurately.  At  regular 
intervals  levels  should  be  run,  and  profiles  made  along  each  line  of 
monuments  showing  the  position  of  the  working  face,  the  original 
position  of  the  surface,  and  the  elevations  at  the  time  of  the  successive 
surveys. 

The  monuments  should  be  located  where  they  will  be  easily  acces- 
sible to  the  surveyor  but  where  they  will  not  be  interfered  with,  and 
they  should  be  so  constructed  that  they  will  not  be  lifted  by  frost.  In 
addition  to  the  levels,  measurements  should  be  made  from  time  to  time 
to  determine  the  amount  of  lateral  movement  or  draw. 

UNDERGROUND    WORK 

It  would  be  essential  that  a  careful  record  be  made  of  underground 
conditions.  In  room-and-pillar  and  panel  work  the  date  of  opening 
rooms,  the  actual  dimensions  of  pillars,  and  the  position  of  the  rooms 
with  regard  to  surface  monuments  should  be  noted.  When  rooms  are 
finished  and  the  pillars  are  drawn,  particular  attention  should  be  given 
to  movements  of  roof  and  floor,  and  if  a  squeeze  follows,  a  detailed 
report  should  be  made  as  a  basis  for  the  study  of  surface  movement  and 
of  other  squeezes. 

^hief  Mining  Engineer,  U.  S.  Bureau  of  Mines,  one  of  the  representatives  of  the 
Bureau    in    this    cooperation. 


108  SURFACE    SUBSIDENCE   IN    ILLINOIS 

After  the  movement  underground  has  ceased,  whatever  observa- 
tions are  possible  should  be  made  in  the  vicinity,  noting  particularly  the 
angle  of  break  in  the  roof,  the  condition  of  pillars,  the  amount  of  open 
space  above  the  falls,  and  the  condition  of  the  roof  material  which  is 
standing. 

In  longwall  mines  the  rate  of  advance  should  be  noted  regularly 
as  well  as  the  stability  and  width  of  the  pack  walls,  the  amount  of 
material  placed  in  the  gob,  the  angle  of  fracture  of  roofs,  the  height 
to  which  breaks  extend  into  the  roof,  the  rate  of  settling  of  the  roof, 
and  the  ratio  of  compression  of  pack  walls.  Observations  should  be 
made  to  discover  the  amount  of  sag  in  a  direction  parallel  to  the  face 
and  between  the  pack  walls. 

If  practicable  the  amount  of  filling  in  one  section  of  the  mine 
should  be  kept  constant,  but  a  different  amount  should  be  used  regularly 
in  another  part,  in  order  to  discover  the  effect  that  filling  has  upon  sub- 
sidence.2 

POSSIBLE   BENEFITS 

From  the  data  secured  it  should  be  feasible  to  determine  the 
amount  of  subsidence  which  may  be  expected  per  foot  of  material  ex- 
cavated at  different  depths  and  with  different  geological  sections.  It 
should  be  possible  to  predict  in  longwall  mining  whether  the  wave  of 
subsidence  will  move  in  advance  of  the  mining  face  or  lag  behind  it. 
The  amount  of  draw  after  the  advance  has  ceased  could  undoubtedly 
be  predicted  with  more  accuracy  than  is  possible  at  present.  The  effect 
of  leaving  pillars  could  probably  be  shown  with  greater  certainty,  and 
it  would  undoubtedly  be  possible  to  protect  such  structures  as  must  be 
left  undisturbed  with  less  interference  with  mining  operations. 

As  previously  noted,  nearly  one-half  the  coal  is  being  left  in  the 
ground  and  made  unavailable  for  future  mining.  At  present  the  lost 
coal  in  the  mines  of  southern  Illinois  represents  a  larger  tonnage  of 
coal  per  acre  than  there  is  in  the  virgin  coal  seam  now  being  mined  in 
northern  Illinois,  and  each  ton  of  this  abandoned  coal  has  a  heating 
value  of  7  to  8  per  cent  greater  than  the  coal  mined  in  northern  Illinois.3 


2This  might  be  feasible  in  a  mine  in  which  the  undercutting  is  done  in  part  by  hand 
and  in  part  by  machines.  In  one  mine  the  ratio  between  the  volume  of  material  removed 
in   the  undercutting  by  machine  is  about  one-fourth  as  much  as  in  undercutting  by  hand. 

sThe  average  analysis  of  58  samples  of  coal  No.  6  from  east  of  the  Duquoin 
anticline  showed  a  heating  value  of  11,825  B.  t.  u.  The  extraction  of  56  per  cent  of  the 
seam  which  averages  9  feet  in  thickness  results  in  leaving  6,732  tons  to  the  acre.  In  northern 
Illinois  the  average  thickness  of  the  coal  mined  is  3  feet  2  inches,  and  the  average  heating 
value,  as  indicated  by  38  samples,  is  10,981  B.  t.  u.  In  other  words,  in  northern  Illinois 
the  virgin  coal  seam  contains  per  acre  5.700  tons  of  coal  of  10,981  B.  t.  u.,  whereas  in 
District  VI  the  average  worked-out  mine  contains  18.1  per  cent  more  coal  of  a  heating 
value  7.7  per  cent  greater  than  does  the  unworked  tract  in  northern   Illinois. 


INVESTIGATIONS    OF    SUBSIDENCE  JQ9 

It  is  hoped  that  a  careful  study  of  the  subsidence  problem  in  the 
various  mining  districts  will  lead  to  a  better  realization  of  the  necessity 
to  the  State  for  extraction  of  the  coal  where  the  damage  to  the  surface 
will  be  reparable.  Where  the  damage  to  the  surface  is  reparable  and  in 
excess  of  the  value  of  the  coal,  the  facts  should  be  made  known  and 
the  proper  steps  taken.  Where  the  damage  to  the  surface  is  irreparable 
and  in  excess  of  the  value  of  the  coal,  it  seems  advisable  to  stop  the 
mining  of  coal  completely  until  such  time  as  the  increased  value  of 
coal  may  be  sufficient  to  warrant  the  renewal  of  mining  and  the  com- 
plete extraction  of  the  coal  possibly  under  improved  methods  of  min- 
ing.4 

The  State  should  give  attention  to  the  problem  of  conservation  in 
those  extensive  areas  of  coal  fields  where  the  right  to  the  coal  is  held 
by  one  party  and  the  surface  by  another,  but  under  the  existing  deed 
the  owner  of  the  coal  is  held  liable  for  any  surface  damage  resulting 
from  mining  operations.  Under  such  conditions  it  may  be  expected 
that  nearly  50  per  cent  of  the  coal  will  be  left  in  the  ground.  Against 
this  practice  a  protest  may  well  be  raised  and  the  State  of  Illinois 
should  find  or  create  a  remedy.5 

t  ♦•*  tGe7™-S'  R^C'  ^  a"  informal  address  in  New  York,  in  1913,  before  the  American 
Institute  of  Mining  Engineers,  stated  that  he  had  been  shown  leveling  data  in  Upper  Silesia, 
Germany  relating  to  surface  elevations  in  and  about  a  certain  important  iron  works,  which 
showed  that  where  granulated  slag  had  been  hydraulically  stowed  in  coal-mine  excavations 
in  a  bed  20  feet  thick  in  which  there  had  been  practically  complete  extraction  of  coal  the 
subsidence  had  not  been  appreciable,  at  the  maximum  point  showing  only  2^  inches  Also 
that  since  the  hydraulic  stowing  system  had  been  inaugurated  in  Westphalia  the  German 
government  had  allowed  mining  under  important  munition  manufacturing  buildings  at  the 
Krupp  works  in  Essen,  whereas  formerly  under  the  old  dry-filling  methods  there  had  been 
serious  subsidence  in  and  about  parts  of  Essen  resulting  in  cracked  walls  and  buildings  which 
he  had   observed  in   1911. 

"It  has  been  suggested  that  a  tax  be  levied  upon  coal  left  in  the  ground.  This  might 
be  done  by  assessing  the  land  or  coal  right  upon  the  full  tonnage  originally  in  the  ground 
less  the  amount  which  has  actually  been  recovered,  and  continuing  this  assessment  against 
the  land  until  the  unmmed  coal  is  recovered.  If  this  were  to  become  the  general  practice 
it  would  undoubtedly  tend  to   induce  the  mining  companies  to  remove  more   of  the  coal 


INDEX 


PAGE 


Agriculture,    effect    of    subsidence 

on    50-61 

Angles  of  break  and  of  draw. 31,  89-93 
Assumption,  mining  at 75 

B 

Belleville  coal,  see  coal  No.  6 
"Blue  band"  coal,  see  coal  No.  6 
Bond  County,   subsidence  in..  73,  85-86 
Brown  County,  subsidence  in. 73,  78-79 
Buildings,  effect  of  subsidence  on. 64-72 
Bunting,      Douglas,      acknowledg- 
ments to 103 

Bureau  County,  subsidence  in. 73,  75-78 


Calhoun  County,  subsidence  in... 

73,78-79 

Canals,  effect  of  subsidence  on.  ..64-65 
Carbondale   formation,  description 

of    ...:..     19 

Carlinville    limestone,     description 

of    22 

Carterville,  subsidence  at 37 

Cass  County,  subsidence  in. .  .73,  78-79 

Caves,  description  of 34-42 

Christian  County,  coal  No.  6  in...     25 

subsidence   in 73,  85-86 

Clark  County,  structure  in 20 

Cleat,  effect  of,  upon  subsidence.  .26-27 

Clinton  County,  coal  No.  6  in 25 

subsidence   in 73,  85-86 

Coal  City,  subsidence  near 43,  65 

Coal  field,  extent  of 15 

"Coal  Measures",  description  of.  18-21 

Coal  No.  1,  production  from 15 

roof  and  floor  of 24 

stratigraohic  position  of 19,  21 

Coal  No.  2,  faults  and  rolls  in 27 

production   from 15 

roof  and  floor  of . ; 24 

strata  associated  with 21 

stratigraphic  position  of 19,  21 

Coal  No.  5,  faults  and  rolls  in... 27-28 

production   from 15 

roof  and  floor  of 25 

Coal  No.  6,  depth  of 21 

faults  and  rolls  in 28-29 

production  from 15 

roof  and  floor  of 25-26 

strata  associated  _  with 22-23 

stratigraphic  position  of 19,  21 

subsidence  above 32 

Coal  No.  7,  faults  and  rolls  in.  . . .     29 

production  from 15 

roof  and  floor  of„ 26 

strata  associated  with 23 


PAGE 

stratigraphic  position  of 19,  21 

Coal  rights,  values  of,  in  Illinois. 55-56 

Compressibility  of  rock 94,  95 

Compression  tests  of  coals 89 

Conservation  of  coal 11, 13 

Cracks,   surface 30-34 

Crushing  strength  of  coals 88-89 

Cuba,  subsidence  near 39 


Damage  caused  by  mining 30-72 

Danville,  subsidence  near 

39,49,59,66,67,86-87 

Dewitt  County,  subsidence  in.  .73,  79-81 

Dewmaine,  subsidence  at 40 

Dikes,  subsidence  associated  with.  38 
Duquoin  anticline 21 

E 

Edgar  County,  subsidence  in..  73,  86-87 
Edwards  County,  structure  of....  19 
Europe,   study  of   subsidence   in..   106 


Faults,  relation  of,  to  subsidence. 27-29 

Fayol,  acknowledgments  to 

93-94,101-102 

Filling  methods 103-105 

Franklin  County,  coal  No.  6  in...     25 

structure  in 20 

subsidence  in 

...  .32,  44,  46,  62,  64,  69,  70,  73,  83-85 

value  of  land  in 52 

Fulton  County,  subsidence  in. 73,  78-81 

G 

Gallatin   County,   subsidence   in. 

73,81-83 

Gobbing,  relation  of,  to  subsidence 

... 103-104 

Greene  County,  subsidence  in. 73,  78-79 
Griffith,  William,  acknowledgments 

to     103-105 

Grundy  County,  subsidence  in. 73,  75-78 

H 

Halbaum,  acknowledgments  to... 91-93 
Hamilton  County,  structure  of . . .  .  19 
Hancock   County,    subsidence   in.. 

. 73,78-79 

Harrisburg,   subsidence   at 37 

Henry  County,  subsidence  in. 73,  78-79 
Herrin  coal,  see  coal  No.  6 


Jackson  County,  subsidence  in 

J ...73,78,83-85 

Vergennes  sandstone  in 21 

Tersey  County,  subsidence  in.  .73,  78-79 


(110) 


INDEX— Continued 


111 


PAGE 


K 


Kentucky,  value  of  land  in. .  .50,  52-54 
Knox  County,  subsidence  in.  ..73,  78-81 


Lands,  values  of 50-61 

La  Salle  anticline 20 

La  Salle  coal,  see  coal  No.  2 

La  Salle  County,  subsidence  in... 

, • 73,75-78,90 

value  of  land  in 52 

La  Salle  _  limestone,     stratigraphic 

position  of 23 

Lawrence  County,  structure  in....'  20 
Logan  County,  subsidence  in . .  73,  79-81 
Longwall   District,   geology  of... 23-24 

subsidence  in 

....  42-43, 48,  64,  71,  73,  75-78, 95-96 
Longwall    mining,    relation    of,    to 

subsidence    30 

M 

Macon  County,  subsidence  in.  .73,  79-81 
Macoupin  County,  coal  No.  6  in . .     25 

subsidence  in 73^  85-86 

Marion  County,  coal  No.  6  in .  . ! .     26 

structure  of 19 

subsidence  in '.'.'.73,  85-86 

Marshall  County,  subsidence  in... 

73  75-78 

Mason  County,  subsidence  in.73,' 79-81 
McDonough  County,  subsidence  in 

7 '3  78-79 

McLean  County,   subsidence  in.' 

^T  _  ••••• 73,79-81 

McLeansboro    formation,    descrip- 
tion of 19 

Madison  County,  coai  No.  6  in...     25 

subsidence  in 73,  85-86 

Menard  County,  subsidence  in.73,  79-81 
Mercer  County,  subsidence  in.73,  78-79 
Montgomery  County,  coal  No.  6  in     26 

subsidence  in 49,  73,  85-86 

Morgan  County,  subsidence  in.73,  78-79 
Moultrie  County,  coal  No.  6,  in.  . .     26 

structure  of 19 

subsidence  in ....73,  85-86 

Murphysboro  coal,  see  coal  No.  2 

N 

New      Haven      limestone,      strati- 
graphic    position    of 22 

Nokomis,   subsidence  near 49 


PAGE 


Pillars,  relation  of,  to  subsidence. 

p.    ,•  •••••........; 100-103 

Pit  holes,  description  of 34-42 

Pottsville     formation,     description 

„     ,of   ;••••• 18-19 

r roduction  of  coal 15-17 

Protection  of  surface .88-105 

Putnam  County,  subsidence  in.73,  75-78 

R 

Railroads,  effect  of  subsidence  on 

Randolph  County,  coal  No*.  6  in.'.     26 

subsidence   in 7^  85-86 

Kice    US.,  acknowledgments  to..   107 

Kichland  County,  structure  of 19 

j   Roads,  effect  of  subsidence  on 64 

I    Rock  Island  coal,  see  coal  No.  1 
Rock  Island  County,  subsidence  in 

p  „  ••••••;..... 73,78-79 

Kolls,  relation  of,  to  subsidence.  .27-29 
Room-and-pillar    mining,     relation 
of,  to  subsidence 30 


Peoria  County,  subsidence  in.  .73,  79-81 
Pennsylvania,  value  of  land  in.. 50,  54 
Pennsylvanian    series,    description 

o£    18-21 

Perry  County,  coal  No.  6  in 26 

subsidence   in 43,  45,  73,  83-86 

Piatt  County,  structure  of 19 


"Safe  depth"  theory 93 

Sags,  description  of '.'.42-50 

St.  Clair  County,  coal  No.  6  in .         26 

subsidence   in 73,85-86 

Valine  County,  subsidence  in..  73,  81-83 

structure  in 20 

Sangamon  County,  coal  No.  6  in. .     26 

structure    of 19 

subsidence  in '.'.73,  79-81, 85-86 

value  of  land  in 52 

Schuyler  County,  subsidence  in... 

73,78-81 

Scott  County,  subsidence  in.. 73,  78-79 
Sewers,  effect  of  subsidence  on.. 69-71 

Shafts,  depths  of 17  ig 

Shawneetown  fault '  20 

Shelby  County,  coal  No.  6  in 26 

subsidence  in 7^  85-86 

Mioal  Creek  limestone,  description 

.of    22 

Springfield,  subsidence  in 68 

Streams,  effect  of  subsidence  on. 64-65 
Streator,  subsidence  near.  .41,  60,  66,  68 
Streets,  effect  of  subsidence  on.. 69-71 
Structure  of  "Coal  Measures".  ..  19-21 
Subsidence,  damage  caused  by... 28-72 

data   on 73-87 

evidences  of WW.  .30-50 

geological   conditions   affecting.' 18-29 

investigations  of 106-109 

protection  against 88-105 

T 

Tazewell  County,  subsidence  in. 

73,79-81 

Third  Vein  coal,  see  coal  No.  2 
Transportation,  relation  of,  to  sub- 
sidence   61-65 


112 


INDEX — Continued 


PAGE 


U 


United  States,  study  of  subsidence 

in    106 


Vermilion  County,  subsidence  in.. 

39,47,49,59,73,86-87 

value  of  land  in 52 

Vergennes      sandstone,      strati- 

graphic  position  of 21 

Virginia,  value  of  land  in 54 

W 

Wachsmann,    acknowledgments    to 

31,91 


Warren  County,  subsidence  in. 73,  78-79 
Washington  County,  coal  No.  6  in    26 

subsidence   in 73,  85-86 

Water  supply,  effect  of  subsidence 

on    .    .     71-72 

Wayne  County,  structure  of 19 

West  Virginia,  value  of  land  in..  50,  54 

White   County,   structure   of 19 

Will  County,  subsidence  in 73,  75-78 

Williamson  County,  coal  No.  6  in.     25 

subsidence   in 63,  73,  83-85 

value  of  land  in 52 

Woodford  County,  subsidence  in. 

73,75-78,79-81 


